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.IO;
using System.Linq;
using System.Numerics;
using System.Reflection.Metadata;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading;

namespace AtCoder
{
	public class Program
	{
		static void Main()
		{
			var cin = new Scanner();
			var (h, w) = cin.Int2();

			int inf = 100000000;
			var src = Helper.Array(w, x => (x, x));
			var seg = new LazySegmentTree<(int start, int end), int?>(
				src,
				(-inf, inf),
				null,
				(x, y) => (x.end - x.start) < (y.end - y.start) ? x : y,
				(x, y, n) => y is null ? x : (y.Value, x.end),
				(x, y) => y is null ? x : y);

			var sb = new StringBuilder();
			for (int i = 0; i < h; i++) {
				var (a, b) = cin.Int2(-1);

				var index = seg.FindRightest(a, b + 1, x => x.start >= 0);
				if(index >= a){
					var cur = seg[index];
					if (b == w - 1) {
						seg.Update(a, b + 1, -inf);
					} else {
						seg.Update(a, b + 1, -inf);
						var next = seg.Query(b + 1);
						if (next.start < 0) {
							seg.Update(b + 1, cur.start);
						}
					}
				}

				var ans = seg.Query(0, w);
				if (ans.start < 0) {
					sb.AppendLine("-1");
				} else {
					sb.AppendLine((ans.end - ans.start + i + 1).ToString());
				}
			}

			Console.Write(sb.ToString());
		}
	}

	public class LazySegmentTree<TData, TUpdate> : IEnumerable<TData>
	{
		private readonly int n_;
		private readonly TData[] data_;
		private readonly TUpdate[] lazy_;
		private readonly Func<TData, TData, TData> operate_;
		private readonly Func<TData, TUpdate, int, TData> update_;
		private readonly Func<TUpdate, TUpdate, TUpdate> compose_;
		private readonly TData unitData_;
		private readonly TUpdate unitUpdate_;

		public int Count { get; }

		public TData this[int index] => Query(index);

		public LazySegmentTree(
			int count,
			TData unitData,
			TUpdate unitUpdate,
			Func<TData, TData, TData> operate,
			Func<TData, TUpdate, int, TData> update,
			Func<TUpdate, TUpdate, TUpdate> compose)
		{
			Count = count;
			n_ = 1;
			while (n_ < count) {
				n_ <<= 1;
			}

			data_ = new TData[n_ << 1];
			for (int i = 0; i < data_.Length; i++) {
				data_[i] = unitData;
			}

			lazy_ = new TUpdate[n_ << 1];
			for (int i = 0; i < lazy_.Length; i++) {
				lazy_[i] = unitUpdate;
			}

			unitData_ = unitData;
			unitUpdate_ = unitUpdate;
			operate_ = operate;
			update_ = update;
			compose_ = compose;
		}

		public LazySegmentTree(
			IReadOnlyList<TData> src,
			TData unitData,
			TUpdate unitUpdate,
			Func<TData, TData, TData> operate,
			Func<TData, TUpdate, int, TData> update,
			Func<TUpdate, TUpdate, TUpdate> compose)
			: this(src.Count, unitData, unitUpdate, operate, update, compose)
		{
			for (int i = 0; i < src.Count; i++) {
				data_[i + n_] = src[i];
			}

			for (int i = n_ - 1; i > 0; --i) {
				data_[i] = operate_(data_[i << 1], data_[(i << 1) + 1]);
			}
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public void Update(int v, TUpdate value)
			=> Update(v, v + 1, value);
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public void Update(Range range, TUpdate value)
			=> Update(range.Start.Value, range.End.Value, value);
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public void Update(int left, int right, TUpdate value)
			=> UpdateCore(left, right, 1, 0, n_, value);
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		private TData UpdateCore(int left, int right, int v, int l, int r, TUpdate value)
		{
			Propagate(v, l, r);
			if (left <= l && r <= right) {
				lazy_[v] = value;
				data_[v] = update_(data_[v], lazy_[v], r - l);
				return data_[v];
			} else if (r <= left || right <= l) {
				return data_[v];
			} else {
				int lc = v << 1;
				int rc = (v << 1) + 1;
				int mid = (l + r) >> 1;
				data_[v] = operate_(
					UpdateCore(left, right, lc, l, mid, value),
					UpdateCore(left, right, rc, mid, r, value));
				return data_[v];
			}
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public TData Query(int v) => Query(v, v + 1);
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public TData Query(Range range) => Query(range.Start.Value, range.End.Value);
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public TData Query(int left, int right)
			=> QueryCore(left, right, 1, 0, n_);
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		private TData QueryCore(int left, int right, int v, int l, int r)
		{
			Propagate(v, l, r);
			if (left <= l && r <= right) {
				return data_[v];
			} else if (r <= left || right <= l) {
				return unitData_;
			} else {
				int lc = v << 1;
				int rc = (v << 1) + 1;
				int mid = (l + r) >> 1;
				return operate_(
					QueryCore(left, right, lc, l, mid),
					QueryCore(left, right, rc, mid, r)
				);
			}
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public int FindLeftest(Range range, Func<TData, bool> check)
			=> FindLeftest(range.Start.Value, range.End.Value, check);
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public int FindLeftest(int left, int right, Func<TData, bool> check)
			=> FindLeftestCore(left, right, 1, 0, n_, check);
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		private int FindLeftestCore(int left, int right, int v, int l, int r, Func<TData, bool> check)
		{
			if (check(data_[v]) == false || r <= left || right <= l) {
				return right;
			} else if (v >= n_) {
				return v - n_;
			} else {
				int lc = v << 1;
				int rc = (v << 1) + 1;
				int mid = (l + r) >> 1;
				Propagate(v, l, r);

				int vl = FindLeftestCore(left, right, lc, l, mid, check);
				if (vl != right) {
					return vl;
				} else {
					return FindLeftestCore(left, right, rc, mid, r, check);
				}
			}
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public int FindRightest(Range range, Func<TData, bool> check)
			=> FindRightest(range.Start.Value, range.End.Value, check);
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public int FindRightest(int left, int right, Func<TData, bool> check)
			=> FindRightestCore(left, right, 1, 0, n_, check);
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		private int FindRightestCore(int left, int right, int v, int l, int r, Func<TData, bool> check)
		{
			if (check(data_[v]) == false || r <= left || right <= l) {
				return left - 1;
			} else if (v >= n_) {
				return v - n_;
			} else {
				int lc = v << 1;
				int rc = (v << 1) + 1;
				int mid = (l + r) >> 1;
				Propagate(v, l, r);

				int vr = FindRightestCore(left, right, rc, mid, r, check);
				if (vr != left - 1) {
					return vr;
				} else {
					return FindRightestCore(left, right, lc, l, mid, check);
				}
			}
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		private void Propagate(int v, int l, int r)
		{
			if (v < n_) {
				int lc = v << 1;
				int rc = (v << 1) + 1;
				int mid = (l + r) >> 1;
				lazy_[lc] = compose_(lazy_[lc], lazy_[v]);
				lazy_[rc] = compose_(lazy_[rc], lazy_[v]);
			}

			data_[v] = update_(data_[v], lazy_[v], r - l);
			lazy_[v] = unitUpdate_;
		}

		public IEnumerator<TData> GetEnumerator()
		{
			for (int i = 0; i < Count; i++) {
				yield return this[i];
			}
		}

		IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
	};

	public class HashMap<TKey, TValue> : Dictionary<TKey, TValue>
	{
		private readonly Func<TKey, TValue> initialzier_;
		public HashMap(Func<TKey, TValue> initialzier)
			: base()
		{
			initialzier_ = initialzier;
		}

		public HashMap(Func<TKey, TValue> initialzier, int capacity)
			: base(capacity)
		{
			initialzier_ = initialzier;
		}

		new public TValue this[TKey key]
		{
			get
			{
				if (ContainsKey(key) == false) {
					base[key] = initialzier_(key);
				}

				return base[key];
			}

			set { base[key] = value; }
		}
	}

	public struct ModInt
	{
		public const long P = 1000000007;
		//public const long P = 998244353;

		public static ModInt Inverse(ModInt value) => Pow(value, P - 2);
		public static ModInt Pow(ModInt value, long k) => Pow(value.value_, k);
		public static ModInt Pow(long value, long k)
		{
			long ret = 1;
			for (k %= P - 1; k > 0; k >>= 1, value = value * value % P) {
				if ((k & 1) == 1) {
					ret = ret * value % P;
				}
			}
			return new ModInt(ret);
		}

		private long value_;

		public ModInt(long value)
			=> value_ = value;
		public ModInt(long value, bool mods)
		{
			if (mods) {
				value %= P;
				if (value < 0) {
					value += P;
				}
			}

			value_ = value;
		}

		public static ModInt operator +(ModInt lhs, ModInt rhs)
		{
			lhs.value_ = (lhs.value_ + rhs.value_) % P;
			return lhs;
		}
		public static ModInt operator +(long lhs, ModInt rhs)
		{
			rhs.value_ = (lhs + rhs.value_) % P;
			return rhs;
		}
		public static ModInt operator +(ModInt lhs, long rhs)
		{
			lhs.value_ = (lhs.value_ + rhs) % P;
			return lhs;
		}

		public static ModInt operator -(ModInt lhs, ModInt rhs)
		{
			lhs.value_ = (P + lhs.value_ - rhs.value_) % P;
			return lhs;
		}
		public static ModInt operator -(long lhs, ModInt rhs)
		{
			rhs.value_ = (P + lhs - rhs.value_) % P;
			return rhs;
		}
		public static ModInt operator -(ModInt lhs, long rhs)
		{
			lhs.value_ = (P + lhs.value_ - rhs) % P;
			return lhs;
		}

		public static ModInt operator *(ModInt lhs, ModInt rhs)
		{
			lhs.value_ = lhs.value_ * rhs.value_ % P;
			return lhs;
		}
		public static ModInt operator *(long lhs, ModInt rhs)
		{
			rhs.value_ = lhs * rhs.value_ % P;
			return rhs;
		}
		public static ModInt operator *(ModInt lhs, long rhs)
		{
			lhs.value_ = lhs.value_ * rhs % P;
			return lhs;
		}

		public static ModInt operator /(ModInt lhs, ModInt rhs)
		{
			long exp = P - 2;
			while (exp > 0) {
				if (exp % 2 > 0) {
					lhs *= rhs;
				}

				rhs *= rhs;
				exp /= 2;
			}

			return lhs;
		}

		public static implicit operator ModInt(long n) => new ModInt(n, true);
		public long ToLong() => value_;
		public override string ToString() => value_.ToString();
	}

	public static class Helper
	{
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public static void UpdateMin<T>(ref T target, T value) where T : IComparable<T>
			=> target = target.CompareTo(value) > 0 ? value : target;
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public static void UpdateMin<T>(ref T target, T value, Action<T> onUpdated) where T : IComparable<T>
		{
			if (target.CompareTo(value) > 0) {
				target = value;
				onUpdated(value);
			}
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public static void UpdateMax<T>(ref T target, T value) where T : IComparable<T>
			=> target = target.CompareTo(value) < 0 ? value : target;
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public static void UpdateMax<T>(ref T target, T value, Action<T> onUpdated) where T : IComparable<T>
		{
			if (target.CompareTo(value) < 0) {
				target = value;
				onUpdated(value);
			}
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public static T[] Array<T>(int n, Func<int, T> init)
			=> Enumerable.Range(0, n).Select(x => init(x)).ToArray();
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public static List<T> List<T>(int n, Func<int, T> init)
			=> Enumerable.Range(0, n).Select(x => init(x)).ToList();

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public static T[,] Array2<T>(int n, int m, T init)
			where T : struct
		{
			var array = new T[n, m];
			for (int i = 0; i < n; i++) {
				for (int j = 0; j < m; j++) {
					array[i, j] = init;
				}
			}

			return array;
		}
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public static T[,] Array2<T>(int n, int m, Func<int, int, T> initializer)
		{
			var array = new T[n, m];
			for (int i = 0; i < n; i++) {
				for (int j = 0; j < m; j++) {
					array[i, j] = initializer(i, j);
				}
			}

			return array;
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public static T[,,] Array3<T>(int n1, int n2, int n3, T init) 
			where T : struct
		{
			var array = new T[n1, n2, n3];
			for (int i1 = 0; i1 < n1; i1++) {
				for (int i2 = 0; i2 < n2; i2++) {
					for (int i3 = 0; i3 < n3; i3++) {
						array[i1, i2, i3] = init;
					}
				}
			}

			return array;
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public static T[,,,] Array4<T>(int n1, int n2, int n3, int n4, T init) 
			where T : struct
		{
			var array = new T[n1, n2, n3, n4];
			for (int i1 = 0; i1 < n1; i1++) {
				for (int i2 = 0; i2 < n2; i2++) {
					for (int i3 = 0; i3 < n3; i3++) {
						for (int i4 = 0; i4 < n4; i4++) {
							array[i1, i2, i3, i4] = init;
						}
					}
				}
			}

			return array;
		}

		private static readonly int[] delta4_ = { 1, 0, -1, 0, 1 };
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public static void DoAt4(int i, int j, int imax, int jmax, Action<int, int> action)
		{
			for (int dn = 0; dn < 4; dn++) {
				int d4i = i + delta4_[dn];
				int d4j = j + delta4_[dn + 1];
				if ((uint)d4i < (uint)imax && (uint)d4j < (uint)jmax) {
					action(d4i, d4j);
				}
			}
		}

		private static readonly int[] delta8_ = { 1, 0, -1, 0, 1, 1, -1, -1, 1 };
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public static void DoAt8(int i, int j, int imax, int jmax, Action<int, int> action)
		{
			for (int dn = 0; dn < 8; dn++) {
				int d8i = i + delta8_[dn];
				int d8j = j + delta8_[dn + 1];
				if ((uint)d8i < (uint)imax && (uint)d8j < (uint)jmax) {
					action(d8i, d8j);
				}
			}
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public static void ForEachSubBit(int bit, Action<int> action)
		{
			for (int sub = bit; sub >= 0; sub--) {
				sub &= bit;
				action(sub);
			}
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public static string Reverse(string src)
		{
			var chars = src.ToCharArray();
			for (int i = 0, j = chars.Length - 1; i < j; i++, j--) {
				var tmp = chars[i];
				chars[i] = chars[j];
				chars[j] = tmp;
			}
			return new string(chars);
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public static string Join<T>(this IEnumerable<T> values, string separator = "")
			=> string.Join(separator, values);
	}

	public class Scanner
	{
		private readonly char[] delimiter_ = new char[] { ' ' };
		private readonly string filePath_;
		private readonly Func<string> reader_;
		private string[] buf_;
		private int index_;

		public Scanner(string file = "")
		{
			if (string.IsNullOrWhiteSpace(file)) {
				reader_ = Console.ReadLine;
			} else {
				filePath_ = file;
				var fs = new StreamReader(file);
				reader_ = fs.ReadLine;
			}
			buf_ = new string[0];
			index_ = 0;
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public string NextLine() => reader_();
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public string Next()
		{
			if (index_ < buf_.Length) {
				return buf_[index_++];
			}

			string st = reader_();
			while (st == "") {
				st = reader_();
			}

			buf_ = st.Split(delimiter_, StringSplitOptions.RemoveEmptyEntries);
			if (buf_.Length == 0) {
				return Next();
			}

			index_ = 0;
			return buf_[index_++];
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public int Int() => int.Parse(Next());
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public int Int(int offset) => int.Parse(Next()) + offset;
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public (int, int) Int2(int offset = 0) 
			=> (Int(offset), Int(offset));
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public (int, int, int) Int3(int offset = 0) 
			=> (Int(offset), Int(offset), Int(offset));
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public (int, int, int, int) Int4(int offset = 0) 
			=> (Int(offset), Int(offset), Int(offset), Int(offset));
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public int[] ArrayInt(int length, int offset = 0)
		{
			int[] Array = new int[length];
			for (int i = 0; i < length; i++) {
				Array[i] = Int(offset);
			}
			return Array;
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public long Long() => long.Parse(Next());
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public long Long(long offset) => long.Parse(Next()) + offset;
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public (long, long) Long2(long offset = 0)
			=> (Long(offset), Long(offset));
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public (long, long, long) Long3(long offset = 0) 
			=> (Long(offset), Long(offset), Long(offset));
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public (long, long, long, long) Long4(long offset = 0) 
			=> (Long(offset), Long(offset), Long(offset), Long(offset));
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public long[] ArrayLong(int length, long offset = 0)
		{
			long[] Array = new long[length];
			for (int i = 0; i < length; i++) {
				Array[i] = Long(offset);
			}
			return Array;
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public double Double() => double.Parse(Next());
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public double Double(double offset) => double.Parse(Next()) + offset;
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public (double, double) Double2(double offset = 0) 
			=> (Double(offset), Double(offset));
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public (double, double, double) Double3(double offset = 0)
			=> (Double(offset), Double(offset), Double(offset));
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public (double, double, double, double) Double4(double offset = 0)
			=> (Double(offset), Double(offset), Double(offset), Double(offset));
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public double[] ArrayDouble(int length, double offset = 0)
		{
			double[] Array = new double[length];
			for (int i = 0; i < length; i++) {
				Array[i] = Double(offset);
			}
			return Array;
		}

		public void Save(string text)
		{
			if (string.IsNullOrWhiteSpace(filePath_)) {
				return;
			}

			File.WriteAllText(filePath_ + "_output.txt", text);
		}
	}
}