Problem:
Score : 600 points

Problem Statement

There is a grid of squares with H+1 horizontal rows and W vertical columns.

You will start at one of the squares in the top row and repeat moving one square right or down. However, for each integer i from 1 through H, you cannot move down from the A_i-th, (A_i + 1)-th, \ldots, B_i-th squares from the left in the i-th row from the top.

For each integer k from 1 through H, find the minimum number of moves needed to reach one of the squares in the (k+1)-th row from the top. (The starting square can be chosen individually for each case.) If, starting from any square in the top row, none of the squares in the (k+1)-th row can be reached, print -1 instead.

Constraints

1 \leq H,W \leq 2\times 10^5

1 \leq A_i \leq B_i \leq W

Input

Input is given from Standard Input in the following format:

H W
A_1 B_1
A_2 B_2
:
A_H B_H

Output

Print H lines. The i-th line should contain the answer for the case k=i.

Sample Input 1

4 4
2 4
1 1
2 3
2 4

Sample Output 1

1
3
6
-1

Let (i,j) denote the square at the i-th row from the top and j-th column from the left.

For k=1, we need one move such as (1,1) → (2,1).

For k=2, we need three moves such as (1,1) → (2,1) → (2,2) → (3,2).

For k=3, we need six moves such as (1,1) → (2,1) → (2,2) → (3,2) → (3,3) → (3,4) → (4,4).

For k=4, it is impossible to reach any square in the fifth row from the top.

Solution in C# (.NET Core 3.1.201) (judge verdict: Accepted)

using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.Globalization;
using System.IO;
using System.Text;
using System.Linq;

using E = System.Linq.Enumerable;
using System.Threading;

internal partial class Solver {
    public void Run() {
        var h = ni();
        var w = ni();
        var a = new int[h];
        var b = new int[h];
        for (int i = 0; i < h; i++) {
            a[i] = ni() - 1;
            b[i] = ni() - 1;
        }

        var ranges = new MultiSet<(int begin, int end, int value)>();
        ranges.Add((-10, 0, -1000000));

        for (int i = 0; i < w; i++) {
            ranges.Add((i, i + 1, i));
        }

        var seg = new SegmentTree<long>((x, y) => Math.Min(x, y), long.MaxValue);
        seg.Build(w, i => 0);

        for (int i = 0; i < h; i++) {
            var begin = ranges.IndexOfLowerBound((a[i], -1, -1)) - 1;
            var changed = new List<(int begin, int end, int value)>();
            var prev = ranges.At(begin);
            if (b[i] + 1 > prev.end) {
                ranges.Remove(prev);
                prev.end = b[i] + 1;
                ranges.Add(prev);
                if (prev.value >= 0) seg[prev.value] = prev.begin - prev.value;

                var iter = ranges.AtIterator(begin + 1);
                for (; iter != null; iter++) {
                    var val = iter.Value;
                    if (val.begin < prev.end) {
                        changed.Add(val);
                    } else {
                        break;
                    }
                }

                foreach (var c in changed) {
                    ranges.Remove(c);
                    if (c.value >= 0) seg[c.value] = long.MaxValue;
                    var v = c;
                    v.begin = prev.end;
                    if (v.begin < v.end) {
                        ranges.Add(v);
                        if (v.value >= 0) {
                            seg[v.value] = v.begin - v.value;
                        }
                    }
                }
            }
            //ranges.TextDump();
            //E.Range(0, w).Select(j => seg[j]).TextDump();
            var ans = seg.Query(0, seg.Count);
            if (ans <= w) cout.WriteLine(ans + i + 1);
            else cout.WriteLine(-1);
        }
    }


    public static int MoveUntil(int ok, int ng, Predicate<int> predicate) {
        if (ok == ng) throw new Exception();
        while (Math.Abs(ok - ng) > 1) {
            var mid = (ok + ng) >> 1;
            if (predicate(mid)) {
                ok = mid;
            } else {
                ng = mid;
            }
        }
        return ok;
    }

}

public sealed class SegmentTree<TMonoid> {
    public int Count { get; private set; }
    private TMonoid[] _node;
    private readonly TMonoid _identity;
    private readonly Func<TMonoid, TMonoid, TMonoid> _merge;

    public SegmentTree(Func<TMonoid, TMonoid, TMonoid> merge, TMonoid identity) {
        _merge = merge;
        _identity = identity;
    }

    public void Build(IList<TMonoid> array) {
        Build(array.Count, i => array[i]);
    }

    public void Build(int n, Func<int, TMonoid> create) {
        Count = n;

        _node = new TMonoid[2 * Count];

        for (int i = 0; i < n; i++) {
            _node[i + Count] = create(i);
        }

        for (int i = Count - 1; i > 0; i--) {
            _node[i] = _merge(_node[i << 1], _node[i << 1 | 1]);
        }
    }

    public void Set(int index, TMonoid val) {
        int p = index + Count;
        _node[p] = val;
        while (p > 0) {
            p >>= 1;
            _node[p] = _merge(_node[p << 1], _node[p << 1 | 1]);
        }
    }

    public TMonoid Query(int begin, int end) {
        TMonoid lv = _identity, rv = _identity;
        int l = begin + Count;
        int r = end + Count - 1;
        for (; l <= r; l >>= 1, r >>= 1) {
            if ((l & 1) == 1) { lv = _merge(lv, _node[l++]); }
            if ((r & 1) == 0) { rv = _merge(_node[r--], rv); }
        }
        return _merge(lv, rv);
    }

    public TMonoid this[int index] {
        get { return _node[index + Count]; }
        set { Set(index, value); }
    }
};


public partial class MultiSet<T> {
    public readonly LLRBTreeNode<T> End = null;
    private LLRBTreeNode<T> root = null;
    private readonly Comparison<T> _comparer;


    public MultiSet() : this(Comparer<T>.Default.Compare) {
    }

    public MultiSet(Comparison<T> comparer) {
        _comparer = comparer;
        root = End;
    }

    protected virtual bool AllowMultiple { get { return true; } }

    public int Count { get { return root == null ? 0 : root.Count + root.LeftTotalCount + root.RightTotalCount - 1; } }

    private LLRBTreeNode<T> FindNode(T value) {
        var node = root;
        while (node != null) {
            int cmp = Compare(value, node);
            if (cmp == 0) {
                return node;
            }
            node = (cmp < 0) ? node.Left : node.Right;
        }
        return null;
    }

    public void Clear() {
        root = End;
    }

    public bool Contains(T value) {
        var node = FindNode(value);
        return node != null;
    }

    public int CountOf(T value) {
        var node = FindNode(value);
        return node != null ? node.Count : 0;
    }

    public int IndexOfLowerBound(T value) {
        var node = root;
        int index = 0;
        while (node != null) {
            int cmp = Compare(value, node);
            if (cmp <= 0) {
                node = node.Left;
            } else {
                index += node.LeftTotalCount + node.Count;
                node = node.Right;
            }
        }
        return index;
    }

    private int Compare(T value, LLRBTreeNode<T> node) {
        if (node == End) {
            return -1;
        }

        return _comparer(value, node.Value);
    }

    public int IndexOfUpperBound(T value) {
        var node = root;
        int index = 0;
        while (node != null) {
            int cmp = Compare(value, node);
            if (cmp < 0) {
                node = node.Left;
            } else {
                index += node.LeftTotalCount + node.Count;
                node = node.Right;
            }
        }
        return index;
    }

    public T At(int index) {
        var node = root;
        while (node != null) {
            int leftCount = node.LeftTotalCount;
            if (leftCount <= index && index < leftCount + node.Count) {
                return node.Value;
            }

            if (index < leftCount) {
                node = node.Left;
            } else {
                index -= leftCount + node.Count;
                node = node.Right;
            }
        }
        throw new ArgumentOutOfRangeException("index");
    }

    public T Min() {
        return At(0);
    }

    public T Max() {
        return At(Count - 1);
    }

    public LLRBTreeIterator<T> AtIterator(int index) {
        var node = root;
        while (node != null) {
            int leftCount = node.LeftTotalCount;
            if (leftCount <= index && index < leftCount + node.Count) {
                return new LLRBTreeIterator<T>(node, index - leftCount);
            }

            if (index < leftCount) {
                node = node.Left;
            } else {
                index -= leftCount + node.Count;
                node = node.Right;
            }
        }
        throw new ArgumentOutOfRangeException("index");
    }

    public void Add(T value) {
        root = Add(root, value);
        root.Color = LLRBTreeNode<T>.BLACK;
    }

    private LLRBTreeNode<T> Add(LLRBTreeNode<T> h, T value) {
        if (h == null) {
            return new LLRBTreeNode<T>(value);
        }

        int cmp = Compare(value, h);
        if (cmp == 0) {
            if (AllowMultiple) {
                h.Count++;
                FixCount(h);
            }
        } else if (cmp <= 0) {
            h.Left = Add(h.Left, value);
            FixCount(h);
        } else {
            h.Right = Add(h.Right, value);
            FixCount(h);
        }

        if (IsRed(h.Right) && !IsRed(h.Left)) {
            h = RotateLeft(h);
        }

        if (IsRed(h.Left) && IsRed(h.Left.Left)) {
            h = RotateRight(h);
        }

        if (IsRed(h.Left) && IsRed(h.Right)) {
            ColorFlip(h);
        }

        return h;
    }

    private LLRBTreeNode<T> RemoveLeftestNode(LLRBTreeNode<T> h, out LLRBTreeNode<T> leftMost) {
        if (h.Left == null) {
            leftMost = h;
            return null;
        }

        if (!IsRed(h.Left) && !IsRed(h.Left.Left)) {
            h = MoveRedLeft(h);
        }

        h.Left = RemoveLeftestNode(h.Left, out leftMost);
        return FixUp(h);
    }

    private bool TryReduceCount(LLRBTreeNode<T> h, T value, out int num) {
        num = 0;
        if (h == null) {
            return false;
        }

        int cmp = Compare(value, h);
        if (cmp == 0) {
            num = h.Count;
            if (h.Count > 1) {
                h.Count--;
                FixCount(h);
                return true;
            }
            return false;
        }
        if (TryReduceCount((cmp < 0) ? h.Left : h.Right, value, out num)) {
            FixCount(h);
            return true;
        }
        return false;
    }


    public bool Remove(T value) {
        if (AllowMultiple) {
            int num;
            if (TryReduceCount(root, value, out num)) {
                return true;
            }
            if (num == 0) {
                return false;
            }
        } else {
            if (!Contains(value)) {
                return false;
            }
        }

        root = RemoveNode(root, value);
        if (root != null) {
            root.Color = LLRBTreeNode<T>.BLACK;
        }
        return true;
    }

    private LLRBTreeNode<T> RemoveNode(LLRBTreeNode<T> h, T value) {
        if (Compare(value, h) < 0) {
            if (h.Left == null) {
                throw new KeyNotFoundException("value");
            }

            if (!IsRed(h.Left) && !IsRed(h.Left.Left)) {
                h = MoveRedLeft(h);
            }
            h.Left = RemoveNode(h.Left, value);
            FixCount(h);
        } else {
            if (IsRed(h.Left)) {
                h = RotateRight(h);
            }

            if (h.Right == null) {
                if (Compare(value, h) == 0) {
                    return null;
                }

                throw new KeyNotFoundException("value");
            }

            if (!IsRed(h.Right) && !IsRed(h.Right.Left)) {
                h = MoveRedRight(h);
            }

            if (Compare(value, h) == 0) {
                LLRBTreeNode<T> sub;
                h.Right = RemoveLeftestNode(h.Right, out sub);
                h = Substitute(h, sub);
                FixCount(h);
            } else {
                h.Right = RemoveNode(h.Right, value);
                FixCount(h);
            }
        }

        return FixUp(h);
    }

    private static LLRBTreeNode<T> Substitute(LLRBTreeNode<T> node, LLRBTreeNode<T> sub) {
        sub.Parent = node.Parent;
        sub.Left = node.Left;
        sub.Right = node.Right;
        sub.TotalCount = node.TotalCount;
        sub.Color = node.Color;

        if (sub.Parent != null) {
            if (sub.Parent.Left == node) {
                sub.Parent.Left = sub;
            }

            if (sub.Parent.Right == node) {
                sub.Parent.Right = sub;
            }
        }
        if (sub.Left != null) {
            sub.Left.Parent = sub;
        }

        if (sub.Right != null) {
            sub.Right.Parent = sub;
        }

        return sub;
    }

    private static LLRBTreeNode<T> MoveRedLeft(LLRBTreeNode<T> h) {
        ColorFlip(h);

        if (IsRed(h.Right.Left)) {
            h.Right = RotateRight(h.Right);
            FixCount(h);
            h = RotateLeft(h);
            ColorFlip(h);
        }

        return h;
    }

    private static LLRBTreeNode<T> MoveRedRight(LLRBTreeNode<T> h) {
        ColorFlip(h);

        if (IsRed(h.Left.Left)) {
            h = RotateRight(h);
            ColorFlip(h);
        }

        return h;
    }

    private static LLRBTreeNode<T> RotateLeft(LLRBTreeNode<T> h) {
        var x = h.Right;
        h.Right = x.Left;
        x.Left = h;

        x.Color = h.Color;
        h.Color = LLRBTreeNode<T>.RED;
        FixCount(h);
        FixCount(x);
        return x;
    }

    private static LLRBTreeNode<T> RotateRight(LLRBTreeNode<T> h) {
        var x = h.Left;
        h.Left = x.Right;
        x.Right = h;

        x.Color = h.Color;
        h.Color = LLRBTreeNode<T>.RED;
        FixCount(h);
        FixCount(x);
        return x;
    }

    private static bool IsRed(LLRBTreeNode<T> h) {
        return h != null && h.Color == LLRBTreeNode<T>.RED;
    }

    private static void ColorFlip(LLRBTreeNode<T> h) {
        h.Color = !h.Color;
        h.Left.Color = !h.Left.Color;
        h.Right.Color = !h.Right.Color;
    }

    private static LLRBTreeNode<T> FixUp(LLRBTreeNode<T> h) {
        if (IsRed(h.Right)) {
            h = RotateLeft(h);
        }

        if (h.Left != null && IsRed(h.Left) && IsRed(h.Left.Left)) {
            h = RotateRight(h);
        }

        if (IsRed(h.Left) && IsRed(h.Right)) {
            ColorFlip(h);
        }
        FixCount(h);
        return h;
    }

    private static void FixCount(LLRBTreeNode<T> node) {
        node.TotalCount = node.Count + node.LeftTotalCount + node.RightTotalCount;
    }

    public void Debug() {
        if (root != null) {
            root.Debug();
        }
    }
}
public partial class Set<T> : MultiSet<T> { protected override bool AllowMultiple { get { return false; } } }

public class LLRBTreeNode<T> {
    public const bool RED = true;
    public const bool BLACK = false;
    public T Value;
    public bool Color = RED;
    public LLRBTreeNode<T> Parent { get; set; }
    private LLRBTreeNode<T> _left;
    private LLRBTreeNode<T> _right;
    public LLRBTreeNode<T> Left {
        get { return _left; }
        set {
            if (_left != null && _left.Parent == this) {
                _left.Parent = null;
            }

            _left = value;
            if (_left != null) {
                _left.Parent = this;
            }
        }
    }
    public LLRBTreeNode<T> Right {
        get { return _right; }
        set {
            if (_right != null && _right.Parent == this) {
                _right.Parent = null;
            }

            _right = value;
            if (_right != null) {
                _right.Parent = this;
            }
        }
    }
    public int Count = 1;
    public LLRBTreeNode(T value) {
        Value = value;
    }

    public int TotalCount = 1;
    public int LeftTotalCount { get { return Left == null ? 0 : Left.TotalCount; } }
    public int RightTotalCount { get { return Right == null ? 0 : Right.TotalCount; } }

    public void Debug(string indent = "") {
        Console.WriteLine(indent + ":" + Value + " - " + Count + " - " + TotalCount);
        if (Left != null) {
            if (Left.Parent != this) {
                Console.WriteLine("Missing Parent");
            }

            Left.Debug(indent + "L");
        }
        if (Right != null) {
            if (Right.Parent != this) {
                Console.WriteLine("Missing Parent");
            }

            Right.Debug(indent + "R");
        }
    }
}

public class LLRBTreeIterator<T> {
    private readonly LLRBTreeNode<T> _node;
    private readonly int _index;

    public LLRBTreeIterator(LLRBTreeNode<T> node, int index = 0) {
        _node = node;
        _index = index;
    }

    public T Value { get { return _node.Value; } }

    public static LLRBTreeIterator<T> operator ++(LLRBTreeIterator<T> x) {
        return x.GetSuccessor();
    }

    public static LLRBTreeIterator<T> operator --(LLRBTreeIterator<T> x) {
        return x.GetPredecessor();
    }

    private LLRBTreeIterator<T> GetSuccessor() {
        if (_index + 1 < _node.Count) {
            return new LLRBTreeIterator<T>(_node, _index + 1);
        } else {
            LLRBTreeNode<T> current, parent;
            if (_node.Right == null) {
                for (current = _node, parent = _node.Parent; parent != null && parent.Right == current; current = parent, parent = current.Parent) {
                }
                if (parent == null || parent.Count == 0) return null;
                return new LLRBTreeIterator<T>(parent);
            } else {
                for (parent = _node.Right, current = parent.Left; current != null; parent = current, current = parent.Left) {
                }
                if (parent == null || parent.Count == 0) return null;
                return new LLRBTreeIterator<T>(parent);
            }
        }
    }

    private LLRBTreeIterator<T> GetPredecessor() {
        if (0 <= _index - 1) {
            return new LLRBTreeIterator<T>(_node, _index - 1);
        } else {
            LLRBTreeNode<T> current, parent;
            if (_node == null) return null;
            if (_node.Left == null) {
                for (current = _node, parent = _node.Parent; parent != null && parent.Left == current; current = parent, parent = current.Parent) {
                }

                if (parent == null) return null;
                return new LLRBTreeIterator<T>(parent, parent.Count - 1);
            } else {
                for (parent = _node.Left, current = parent.Right; current != null; parent = current, current = parent.Right) {
                }

                if (parent == null) return null;
                return new LLRBTreeIterator<T>(parent, parent.Count - 1);
            }
        }
    }
}

public partial class MultiSet<T> : IEnumerable<T> {
    public IEnumerator<T> GetEnumerator() {
        var node = root;
        var stack = new Stack<LLRBTreeNode<T>>();
        while (node != null || stack.Count > 0) {
            while (node != null) {
                stack.Push(node);
                node = node.Left;
            }
            node = stack.Pop();
            if (node == End) {
                break;
            }

            int count = node.Count;
            for (int i = 0; i < count; i++) {
                yield return node.Value;
            }
            node = node.Right;
        }
    }

    IEnumerator IEnumerable.GetEnumerator() {
        return GetEnumerator();
    }
}
// PREWRITEN CODE BEGINS FROM HERE

static public class StringExtensions {
    static public string JoinToString<T>(this IEnumerable<T> source, string separator = " ") {
        return string.Join(separator, source);
    }
}

internal partial class Solver : Scanner {
    static readonly int? StackSizeInMebiByte = null; //50;
    public static void StartAndJoin(Action action, int maxStackSize) {
        var thread = new Thread(new ThreadStart(action), maxStackSize);
        thread.Start();
        thread.Join();
    }

    public static void Main() {
#if LOCAL
        byte[] inputBuffer = new byte[1000000];
        var inputStream = Console.OpenStandardInput(inputBuffer.Length);
        using (var reader = new StreamReader(inputStream, Console.InputEncoding, false, inputBuffer.Length)) {
            Console.SetIn(reader);
            new Solver(Console.In, Console.Out).Run();
        }
#else
        Console.SetOut(new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false });
        if (StackSizeInMebiByte.HasValue) {
            StartAndJoin(() => new Solver(Console.In, Console.Out).Run(), StackSizeInMebiByte.Value * 1024 * 1024);
        } else {
            new Solver(Console.In, Console.Out).Run();
        }
        Console.Out.Flush();
#endif
    }

#pragma warning disable IDE0052
    private readonly TextReader cin;
    private readonly TextWriter cout;
    private readonly TextWriter cerr;
#pragma warning restore IDE0052

    public Solver(TextReader reader, TextWriter writer)
        : base(reader) {
        cin = reader;
        cout = writer;
        cerr = Console.Error;
    }

    public Solver(string input, TextWriter writer)
        : this(new StringReader(input), writer) {
    }

#pragma warning disable IDE1006
#pragma warning disable IDE0051
    private int ni() { return NextInt(); }
    private int[] ni(int n) { return NextIntArray(n); }
    private long nl() { return NextLong(); }
    private long[] nl(int n) { return NextLongArray(n); }
    private double nd() { return NextDouble(); }
    private double[] nd(int n) { return NextDoubleArray(n); }
    private string ns() { return Next(); }
    private string[] ns(int n) { return NextArray(n); }
#pragma warning restore IDE1006
#pragma warning restore IDE0051
}

#if DEBUG
internal static class LinqPadExtension {
    public static string TextDump<T>(this T obj) {
        if (obj is IEnumerable) return (obj as IEnumerable).Cast<object>().JoinToString().Dump();
        else return obj.ToString().Dump();
    }
    public static T Dump<T>(this T obj) {
        return LINQPad.Extensions.Dump(obj);
    }
}
#endif

public class Scanner {
    private readonly TextReader Reader;
    private readonly CultureInfo ci = CultureInfo.InvariantCulture;

    private readonly char[] buffer = new char[2 * 1024];
    private int cursor = 0, length = 0;
    private string Token;
    private readonly StringBuilder sb = new StringBuilder(1024);

    public Scanner()
        : this(Console.In) {
    }

    public Scanner(TextReader reader) {
        Reader = reader;
    }

    public int NextInt() { return checked((int)NextLong()); }
    public long NextLong() {
        var s = Next();
        long r = 0;
        int i = 0;
        bool negative = false;
        if (s[i] == '-') {
            negative = true;
            i++;
        }
        for (; i < s.Length; i++) {
            r = r * 10 + (s[i] - '0');
#if DEBUG
            if (!char.IsDigit(s[i])) throw new FormatException();
#endif
        }
        return negative ? -r : r;
    }
    public double NextDouble() { return double.Parse(Next(), ci); }
    public string[] NextArray(int size) {
        string[] array = new string[size];
        for (int i = 0; i < size; i++) {
            array[i] = Next();
        }

        return array;
    }
    public int[] NextIntArray(int size) {
        int[] array = new int[size];
        for (int i = 0; i < size; i++) {
            array[i] = NextInt();
        }

        return array;
    }

    public long[] NextLongArray(int size) {
        long[] array = new long[size];
        for (int i = 0; i < size; i++) {
            array[i] = NextLong();
        }

        return array;
    }

    public double[] NextDoubleArray(int size) {
        double[] array = new double[size];
        for (int i = 0; i < size; i++) {
            array[i] = NextDouble();
        }

        return array;
    }

    public string Next() {
        if (Token == null) {
            if (!StockToken()) {
                throw new Exception();
            }
        }
        var token = Token;
        Token = null;
        return token;
    }

    public bool HasNext() {
        if (Token != null) {
            return true;
        }

        return StockToken();
    }

    private bool StockToken() {
        while (true) {
            sb.Clear();
            while (true) {
                if (cursor >= length) {
                    cursor = 0;
                    if ((length = Reader.Read(buffer, 0, buffer.Length)) <= 0) {
                        break;
                    }
                }
                var c = buffer[cursor++];
                if (33 <= c && c <= 126) {
                    sb.Append(c);
                } else {
                    if (sb.Length > 0) break;
                }
            }

            if (sb.Length > 0) {
                Token = sb.ToString();
                return true;
            }

            return false;
        }
    }
}