Problem:
Score : 500 points

Problem Statement

There are N towns on a plane. The i-th town is located at the coordinates (x_i,y_i). There may be more than one town at the same coordinates.

You can build a road between two towns at coordinates (a,b) and (c,d) for a cost of min(|a-c|,|b-d|) yen (the currency of Japan). It is not possible to build other types of roads.

Your objective is to build roads so that it will be possible to travel between every pair of towns by traversing roads. At least how much money is necessary to achieve this?

Constraints

2 ≤ N ≤ 10^5

0 ≤ x_i,y_i ≤ 10^9

All input values are integers.

Input

Input is given from Standard Input in the following format:

N
x_1 y_1
x_2 y_2
:
x_N y_N

Output

Print the minimum necessary amount of money in order to build roads so that it will be possible to travel between every pair of towns by traversing roads.

Sample Input 1

3
1 5
3 9
7 8

Sample Output 1

3

Build a road between Towns 1 and 2, and another between Towns 2 and 3. The total cost is 2+1=3 yen.

Sample Input 2

6
8 3
4 9
12 19
18 1
13 5
7 6

Sample Output 2

8

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.io.*;
import java.util.*;

/**
 * @author baito
 */

class UnionFindTree
{
    int[] par;
    int[] rank;
    int[] sizes;

    UnionFindTree(int n)
    {
        par = new int[n];
        rank = new int[n];
        sizes = new int[n];
        for (int i = 0; i < n; i++)
        {
            par[i] = i;
            sizes[i] = 1;
        }
    }

    int root(int x)
    {
        if (par[x] == x) return x;
        else return par[x] = root(par[x]);
    }

    void unite(int x, int y)
    {
        int rx = root(x);
        int ry = root(y);

        if (rx == ry) return;
        if (rank[rx] < rank[ry])
        {
            par[rx] = ry;
            sizes[ry] += sizes[rx];
        }
        else
        {
            par[ry] = rx;
            sizes[rx] += sizes[ry];
            if (rank[rx] == rank[ry]) rank[rx]++;
        }
    }

    boolean isSame(int x, int y)
    {
        return root(x) == root(y);
    }

    int size(int x)
    {
        return sizes[root(x)];
    }
}

class P implements Comparable<P>
{
    int v, id;

    P(int a, int b)
    {
        v = a;
        id = b;
    }

    @Override
    public boolean equals(Object o)
    {
        if (this == o) return true;
        if (!(o instanceof P)) return false;
        P p = (P) o;
        return v == p.v && id == p.id;
    }

    @Override
    public int hashCode()
    {
        return Objects.hash(v, id);
    }

    @Override
    public int compareTo(P p)
    {
        return v == p.v ? id - p.id : v - p.v; //xで昇順にソート
        //return (v == p.v ? id - p.id : v - p.v) * -1; //xで降順にソート
        //return id == p.id ? v - p.v : id - p.id;//yで昇順にソート
        //return (id == p.id ? v - p.v : id - p.id)*-1;//yで降順にソート
    }
}

@SuppressWarnings("unchecked")
public class Main
{
    static StringBuilder sb = new StringBuilder();
    static FastScanner sc = new FastScanner(System.in);
    static int INF = 1234567890;
    static long LINF = 123456789123456789L;
    static long MINF = -123456789123456789L;
    static long MOD = 1000000007;
    static int[] y4 = {0, 1, 0, -1};
    static int[] x4 = {1, 0, -1, 0};
    static int[] y8 = {0, 1, 0, -1, -1, 1, 1, -1};
    static int[] x8 = {1, 0, -1, 0, 1, -1, 1, -1};
    static long[] Fa;//factorial
    static boolean[] isPrime;
    static int[] primes;
    static char[][] map;

    static int N, M, K;
    static int[] A;

    public static void main(String[] args)
    {
        //longを忘れるなオーバーフローするぞ
        N = sc.nextInt();
        P[] px = new P[N];
        P[] py = new P[N];
        for (int i = 0; i < N; i++)
        {
            px[i] = new P(sc.nextInt(), i);
            py[i] = new P(sc.nextInt(), i);
        }
        Arrays.sort(px);
        Arrays.sort(py);
        for (int i = 0; i < N - 1; i++)
        {
            addEdge(px[i].id, px[i + 1].id, px[i + 1].v - px[i].v);
            addEdge(py[i].id, py[i + 1].id, py[i + 1].v - py[i].v);
        }
        Collections.sort(edges);

        //クラスカル法
        UnionFindTree uni = new UnionFindTree(N);
        long res = 0;
        for (Edge e : edges)
        {
            int f = e.f;
            int t = e.t;
            if (uni.isSame(f, t)) continue;
            uni.unite(f, t);
            res += e.toCost;
        }
        System.out.println(res);
    }

    static ArrayList<Edge> edges = new ArrayList<>();

    public static void addEdge(int f, int t, long c)
    {
        edges.add(new Edge(f, t, c));
    }


    static class Edge implements Comparable<Edge>
    {
        int f;
        int t;
        long toCost;

        Edge(int f, int to, long cost)
        {
            this.f = f;
            t = to;
            toCost = cost;
        }

        @Override
        public int compareTo(Edge e)
        {
            return toCost == e.toCost ? 0 : toCost > e.toCost ? 1 : -1;
        }

    }

    public static int upper0(int a)
    {
        if (a < 0) return 0;
        return a;
    }

    public static long upper0(long a)
    {
        if (a < 0) return 0;
        return a;
    }

    public static Integer[] toIntegerArray(int[] ar)
    {
        Integer[] res = new Integer[ar.length];
        for (int i = 0; i < ar.length; i++)
        {
            res[i] = ar[i];
        }
        return res;
    }

    //k個の次の組み合わせをビットで返す 大きさに上限はない 110110 -> 111001
    public static int nextCombSizeK(int comb, int k)
    {
        int x = comb & -comb; //最下位の1
        int y = comb + x; //連続した下の1を繰り上がらせる
        return ((comb & ~y) / x >> 1) | y;
    }

    public static int keta(long num)
    {
        int res = 0;
        while (num > 0)
        {
            num /= 10;
            res++;
        }
        return res;
    }

    public static long getHashKey(int a, int b)
    {
        return (long) a << 32 | b;
    }

    public static boolean isOutofIndex(int x, int y)
    {
        if (x < 0 || y < 0) return true;
        if (map[0].length <= x || map.length <= y) return true;
        return false;
    }

    public static void setPrimes()
    {
        int n = 100001;
        isPrime = new boolean[n];
        List<Integer> prs = new ArrayList<>();
        Arrays.fill(isPrime, true);
        isPrime[0] = isPrime[1] = false;
        for (int i = 2; i * i <= n; i++)
        {
            if (!isPrime[i]) continue;
            prs.add(i);
            for (int j = i * 2; j < n; j += i)
            {
                isPrime[j] = false;
            }
        }
        primes = new int[prs.size()];
        for (int i = 0; i < prs.size(); i++)
            primes[i] = prs.get(i);
    }

    public static void revSort(int[] a)
    {
        Arrays.sort(a);
        reverse(a);
    }

    public static void revSort(long[] a)
    {
        Arrays.sort(a);
        reverse(a);
    }

    public static int[][] copy(int[][] ar)
    {
        int[][] nr = new int[ar.length][ar[0].length];
        for (int i = 0; i < ar.length; i++)
            for (int j = 0; j < ar[0].length; j++)
                nr[i][j] = ar[i][j];
        return nr;
    }

    /**
     * <h1>指定した値以上の先頭のインデクスを返す</h1>
     * <p>配列要素が０のときは、０が返る。</p>
     *
     * @return<b>int</b> ： 探索した値以上で、先頭になるインデクス
     * 値が無ければ、挿入できる最小のインデックス
     */
    public static int lowerBound(final int[] arr, final int value)
    {
        int low = 0;
        int high = arr.length;
        int mid;

        while (low < high)
        {
            mid = ((high - low) >>> 1) + low;    //(low + high) / 2 (オーバーフロー対策)
            if (arr[mid] < value)
            {
                low = mid + 1;
            }
            else
            {
                high = mid;
            }
        }
        return low;
    }

    /**
     * <h1>指定した値より大きい先頭のインデクスを返す</h1>
     * <p>配列要素が０のときは、０が返る。</p>
     *
     * @return<b>int</b> ： 探索した値より上で、先頭になるインデクス
     * 値が無ければ、挿入できる最小のインデックス
     */
    public static int upperBound(final int[] arr, final int value)
    {
        int low = 0;
        int high = arr.length;
        int mid;
        while (low < high)
        {
            mid = ((high - low) >>> 1) + low;    //(low + high) / 2 (オーバーフロー対策)
            if (arr[mid] <= value)
            {
                low = mid + 1;
            }
            else
            {
                high = mid;
            }
        }
        return low;
    }

    /**
     * <h1>指定した値以上の先頭のインデクスを返す</h1>
     * <p>配列要素が０のときは、０が返る。</p>
     *
     * @return<b>int</b> ： 探索した値以上で、先頭になるインデクス
     * 値がなければ挿入できる最小のインデックス
     */
    public static long lowerBound(final long[] arr, final long value)
    {
        int low = 0;
        int high = arr.length;
        int mid;
        while (low < high)
        {
            mid = ((high - low) >>> 1) + low;    //(low + high) / 2 (オーバーフロー対策)
            if (arr[mid] < value)
            {
                low = mid + 1;
            }
            else
            {
                high = mid;
            }
        }
        return low;
    }

    /**
     * <h1>指定した値より大きい先頭のインデクスを返す</h1>
     * <p>配列要素が０のときは、０が返る。</p>
     *
     * @return<b>int</b> ： 探索した値より上で、先頭になるインデクス
     * 値がなければ挿入できる最小のインデックス
     */
    public static long upperBound(final long[] arr, final long value)
    {
        int low = 0;
        int high = arr.length;
        int mid;
        while (low < high)
        {
            mid = ((high - low) >>> 1) + low;    //(low + high) / 2 (オーバーフロー対策)
            if (arr[mid] <= value)
            {
                low = mid + 1;
            }
            else
            {
                high = mid;
            }
        }
        return low;
    }

    //次の順列に書き換える、最大値ならfalseを返す
    public static boolean nextPermutation(int A[])
    {
        int len = A.length;
        int pos = len - 2;
        for (; pos >= 0; pos--)
        {
            if (A[pos] < A[pos + 1]) break;
        }
        if (pos == -1) return false;

        //posより大きい最小の数を二分探索
        int ok = pos + 1;
        int ng = len;
        while (Math.abs(ng - ok) > 1)
        {
            int mid = (ok + ng) / 2;
            if (A[mid] > A[pos]) ok = mid;
            else ng = mid;

        }

        swap(A, pos, ok);
        reverse(A, pos + 1, len - 1);


        return true;
    }

    //次の順列に書き換える、最小値ならfalseを返す
    public static boolean prevPermutation(int A[])
    {
        int len = A.length;
        int pos = len - 2;
        for (; pos >= 0; pos--)
        {
            if (A[pos] > A[pos + 1]) break;
        }
        if (pos == -1) return false;

        //posより小さい最大の数を二分探索
        int ok = pos + 1;
        int ng = len;
        while (Math.abs(ng - ok) > 1)
        {
            int mid = (ok + ng) / 2;
            if (A[mid] < A[pos]) ok = mid;
            else ng = mid;

        }

        swap(A, pos, ok);
        reverse(A, pos + 1, len - 1);


        return true;
    }

    //↓nCrをmod計算するために必要。　***factorial(N)を呼ぶ必要がある***
    static long ncr(int n, int r)
    {
        if (n < r) return 0;
        else if (r == 0) return 1;

        factorial(n);
        return Fa[n] / (Fa[n - r] * Fa[r]);
    }

    static long ncr2(int a, int b)
    {
        if (b == 0) return 1;
        else if (a < b) return 0;
        long res = 1;
        for (int i = 0; i < b; i++)
        {
            res *= a - i;
            res /= i + 1;
        }
        return res;
    }

    static long ncrdp(int n, int r)
    {
        if (n < r) return 0;
        long[][] dp = new long[n + 1][r + 1];
        for (int ni = 0; ni < n + 1; ni++)
        {
            dp[ni][0] = dp[ni][ni] = 1;
            for (int ri = 1; ri < ni; ri++)
            {
                dp[ni][ri] = dp[ni - 1][ri - 1] + dp[ni - 1][ri];
            }
        }
        return dp[n][r];
    }

    static long modNcr(int n, int r)
    {
        if (n < r) return 0;
        long result = Fa[n];
        result = result * modInv(Fa[n - r]) % MOD;
        result = result * modInv(Fa[r]) % MOD;
        return result;
    }

    public static long modSum(long... lar)
    {
        long res = 0;
        for (long l : lar)
            res = (res + l % MOD) % MOD;
        if (res < 0) res += MOD;
        res %= MOD;
        return res;
    }

    public static long modDiff(long a, long b)
    {
        long res = a % MOD - b % MOD;
        if (res < 0) res += MOD;
        res %= MOD;
        return res;
    }

    public static long modMul(long... lar)
    {
        long res = 1;
        for (long l : lar)
            res = (res * l % MOD) % MOD;
        if (res < 0) res += MOD;
        res %= MOD;
        return res;
    }

    public static long modDiv(long a, long b)
    {
        long x = a % MOD;
        long y = b % MOD;
        long res = (x * modInv(y)) % MOD;
        return res;
    }

    static long modInv(long n)
    {
        return modPow(n, MOD - 2);
    }

    static void factorial(int n)
    {
        Fa = new long[n + 1];
        Fa[0] = Fa[1] = 1;
//        for (int i = 2; i <= n; i++)
//        {
//            Fa[i] = (Fa[i - 1] * i) % MOD;
//        }
        //
        for (int i = 2; i <= 100000; i++)
        {
            Fa[i] = (Fa[i - 1] * i) % MOD;
        }
        for (int i = 100001; i <= n; i++)
        {
            Fa[i] = (Fa[i - 1] * i) % MOD;
        }
    }

    static long modPow(long x, long n)
    {
        long res = 1L;
        while (n > 0)
        {
            if ((n & 1) == 1)
            {
                res = res * x % MOD;
            }
            x = x * x % MOD;
            n >>= 1;
        }
        return res;
    }

    //↑nCrをmod計算するために必要

    static int gcd(int n, int r)
    {
        return r == 0 ? n : gcd(r, n % r);
    }

    static long gcd(long n, long r)
    {
        return r == 0 ? n : gcd(r, n % r);
    }

    static <T> void swap(T[] x, int i, int j)
    {
        T t = x[i];
        x[i] = x[j];
        x[j] = t;
    }

    static void swap(int[] x, int i, int j)
    {
        int t = x[i];
        x[i] = x[j];
        x[j] = t;
    }

    public static void reverse(int[] x)
    {
        int l = 0;
        int r = x.length - 1;
        while (l < r)
        {
            int temp = x[l];
            x[l] = x[r];
            x[r] = temp;
            l++;
            r--;
        }
    }

    public static void reverse(long[] x)
    {
        int l = 0;
        int r = x.length - 1;
        while (l < r)
        {
            long temp = x[l];
            x[l] = x[r];
            x[r] = temp;
            l++;
            r--;
        }
    }

    public static void reverse(char[] x)
    {
        int l = 0;
        int r = x.length - 1;
        while (l < r)
        {
            char temp = x[l];
            x[l] = x[r];
            x[r] = temp;
            l++;
            r--;
        }
    }

    public static void reverse(int[] x, int s, int e)
    {
        int l = s;
        int r = e;
        while (l < r)
        {
            int temp = x[l];
            x[l] = x[r];
            x[r] = temp;
            l++;
            r--;
        }
    }

    static int length(int a)
    {
        int cou = 0;
        while (a != 0)
        {
            a /= 10;
            cou++;
        }
        return cou;
    }

    static int length(long a)
    {
        int cou = 0;
        while (a != 0)
        {
            a /= 10;
            cou++;
        }
        return cou;
    }

    static int cou(boolean[] a)
    {
        int res = 0;
        for (boolean b : a)
        {
            if (b) res++;
        }
        return res;
    }

    static int cou(String s, char c)
    {
        int res = 0;
        for (char ci : s.toCharArray())
        {
            if (ci == c) res++;
        }
        return res;
    }

    static int countC2(char[][] a, char c)
    {
        int co = 0;
        for (int i = 0; i < a.length; i++)
            for (int j = 0; j < a[0].length; j++)
                if (a[i][j] == c) co++;
        return co;
    }

    static int countI(int[] a, int key)
    {
        int co = 0;
        for (int i = 0; i < a.length; i++)
            if (a[i] == key) co++;
        return co;
    }

    static int countI(int[][] a, int key)
    {
        int co = 0;
        for (int i = 0; i < a.length; i++)
            for (int j = 0; j < a[0].length; j++)
                if (a[i][j] == key) co++;
        return co;
    }

    static void fill(int[][] a, int v)
    {
        for (int i = 0; i < a.length; i++)
            for (int j = 0; j < a[0].length; j++)
                a[i][j] = v;
    }


    static void fill(long[][] a, long v)
    {
        for (int i = 0; i < a.length; i++)
            for (int j = 0; j < a[0].length; j++)
                a[i][j] = v;
    }

    static void fill(int[][][] a, int v)
    {
        for (int i = 0; i < a.length; i++)
            for (int j = 0; j < a[0].length; j++)
                for (int k = 0; k < a[0][0].length; k++)
                    a[i][j][k] = v;
    }

    static int max(int... a)
    {
        int res = Integer.MIN_VALUE;
        for (int i : a)
        {
            res = Math.max(res, i);
        }
        return res;
    }

    static long min(long... a)
    {
        long res = Long.MAX_VALUE;
        for (long i : a)
        {
            res = Math.min(res, i);
        }
        return res;
    }

    static int max(int[][] ar)
    {
        int res = Integer.MIN_VALUE;
        for (int i[] : ar)
            res = Math.max(res, max(i));
        return res;
    }

    static int min(int... a)
    {
        int res = Integer.MAX_VALUE;
        for (int i : a)
        {
            res = Math.min(res, i);
        }
        return res;
    }


    static int min(int[][] ar)
    {
        int res = Integer.MAX_VALUE;
        for (int i[] : ar)
            res = Math.min(res, min(i));
        return res;
    }

    static int sum(int[] a)
    {
        int cou = 0;
        for (int i : a)
            cou += i;
        return cou;
    }

    static int abs(int a)
    {
        return Math.abs(a);
    }

    static class FastScanner
    {

        private BufferedReader reader = null;
        private StringTokenizer tokenizer = null;

        public FastScanner(InputStream in)
        {
            reader = new BufferedReader(new InputStreamReader(in));
            tokenizer = null;
        }

        public String next()
        {
            if (tokenizer == null || !tokenizer.hasMoreTokens())
            {
                try
                {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e)
                {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        /*public String nextChar(){
            return (char)next()[0];
        }*/
        public String nextLine()
        {
            if (tokenizer == null || !tokenizer.hasMoreTokens())
            {
                try
                {
                    return reader.readLine();
                } catch (IOException e)
                {
                    throw new RuntimeException(e);
                }
            }

            return tokenizer.nextToken("\n");
        }

        public long nextLong()
        {
            return Long.parseLong(next());
        }

        public int nextInt()
        {
            return Integer.parseInt(next());
        }

        public double nextDouble()
        {
            return Double.parseDouble(next());
        }

        public int[] nextIntArray(int n)
        {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
            {
                a[i] = nextInt();
            }
            return a;
        }

        public int[] nextIntArrayOneIndex(int n)
        {
            int[] a = new int[n + 1];
            for (int i = 1; i < n + 1; i++)
            {
                a[i] = nextInt();
            }
            return a;
        }

        public int[] nextIntArrayDec(int n)
        {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
            {
                a[i] = nextInt() - 1;
            }
            return a;
        }

        public int[][] nextIntArray2(int h, int w)
        {
            int[][] a = new int[h][w];
            for (int hi = 0; hi < h; hi++)
            {
                for (int wi = 0; wi < w; wi++)
                {
                    a[hi][wi] = nextInt();
                }
            }
            return a;
        }

        public int[][] nextIntArray2Dec(int h, int w)
        {
            int[][] a = new int[h][w];
            for (int hi = 0; hi < h; hi++)
            {
                for (int wi = 0; wi < w; wi++)
                {
                    a[hi][wi] = nextInt() - 1;
                }
            }
            return a;
        }

        //複数の配列を受け取る
        public void nextIntArrays2ar(int[] a, int[] b)
        {
            for (int i = 0; i < a.length; i++)
            {
                a[i] = sc.nextInt();
                b[i] = sc.nextInt();
            }
        }

        public void nextIntArrays2arDec(int[] a, int[] b)
        {
            for (int i = 0; i < a.length; i++)
            {
                a[i] = sc.nextInt() - 1;
                b[i] = sc.nextInt() - 1;
            }
        }

        //複数の配列を受け取る
        public void nextIntArrays3ar(int[] a, int[] b, int[] c)
        {
            for (int i = 0; i < a.length; i++)
            {
                a[i] = sc.nextInt();
                b[i] = sc.nextInt();
                c[i] = sc.nextInt();
            }
        }

        //複数の配列を受け取る
        public void nextIntArrays3arDecLeft2(int[] a, int[] b, int[] c)
        {
            for (int i = 0; i < a.length; i++)
            {
                a[i] = sc.nextInt() - 1;
                b[i] = sc.nextInt() - 1;
                c[i] = sc.nextInt();
            }
        }

        public Integer[] nextIntegerArray(int n)
        {
            Integer[] a = new Integer[n];
            for (int i = 0; i < n; i++)
            {
                a[i] = nextInt();
            }
            return a;
        }

        public char[] nextCharArray(int n)
        {
            char[] a = next().toCharArray();

            return a;
        }

        public char[][] nextCharArray2(int h, int w)
        {
            char[][] a = new char[h][w];
            for (int i = 0; i < h; i++)
            {
                a[i] = next().toCharArray();
            }
            return a;
        }

        //スペースが入っている場合
        public char[][] nextCharArray2s(int h, int w)
        {
            char[][] a = new char[h][w];
            for (int i = 0; i < h; i++)
            {
                a[i] = nextLine().replace(" ", "").toCharArray();
            }
            return a;
        }

        public char[][] nextWrapCharArray2(int h, int w, char c)
        {
            char[][] a = new char[h + 2][w + 2];
            //char c = '*';
            int i;
            for (i = 0; i < w + 2; i++)
                a[0][i] = c;
            for (i = 1; i < h + 1; i++)
            {
                a[i] = (c + next() + c).toCharArray();
            }
            for (i = 0; i < w + 2; i++)
                a[h + 1][i] = c;
            return a;
        }

        //スペースが入ってる時用
        public char[][] nextWrapCharArray2s(int h, int w, char c)
        {
            char[][] a = new char[h + 2][w + 2];
            //char c = '*';
            int i;
            for (i = 0; i < w + 2; i++)
                a[0][i] = c;
            for (i = 1; i < h + 1; i++)
            {
                a[i] = (c + nextLine().replace(" ", "") + c).toCharArray();
            }
            for (i = 0; i < w + 2; i++)
                a[h + 1][i] = c;
            return a;
        }

        public long[] nextLongArray(int n)
        {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
            {
                a[i] = nextLong();
            }
            return a;
        }

        public long[][] nextLongArray2(int h, int w)
        {
            long[][] a = new long[h][w];
            for (int hi = 0; hi < h; hi++)
            {
                for (int wi = 0; wi < w; wi++)
                {
                    a[hi][wi] = nextLong();
                }
            }
            return a;
        }
    }
}