做一次修改，会把所有的x变成y
    问要做多少次修改，才能保证两个数组中的数字是一样的

    1. package test.meituan;
    3. import java.util.Scanner;
    5. public class Main4 {
    6.   static class UF {
    7.     private int[] parent;
    9.     public UF(int n) {
    10.       parent = new int[n];
    11.       for (int i = 0; i < n; i++) {
    12.         parent[i] = i;
    13.       }
    14.     }
    16.     public void union(int p, int q) {
    17.       int rootP = find(p);
    18.       int rootQ = find(q);
    19.       if (rootP == rootQ)
    20.         return;
    21.       parent[rootP] = rootQ;
    22.     }
    24.     public boolean connected(int p, int q) {
    25.       int rootP = find(p);
    26.       int rootQ = find(q);
    27.       return rootP == rootQ;
    28.     }
    30.     private int find(int x) {
    31.       if (x != parent[x]) {
    32.         int p = parent[x];
    33.         parent[x] = find(p);
    34.       }
    35.       return parent[x];
    36.     }
    37.   }
    39.   public static void main(String[] args) {
    40.     Scanner in = new Scanner(System.in);
    41.     int n = in.nextInt();
    42.     int[] left = new int[n / 2];
    43.     int[] right = new int[n / 2];
    44.     for (int i = 0; i < n / 2; i++) {
    45.       left[i] = in.nextInt();
    46.     }
    47.     for (int i = 0; i < n / 2; i++) {
    48.       right[i] = in.nextInt();
    49.     }
    50.     UF uf = new UF(100000);
    51.     long modify = 0;
    52.     for (int i = 0; i < n / 2; i++) {
    53.       if (!uf.connected(left[i], right[i])) {
    54.         uf.union(left[i], right[i]);
    55.         modify++;
    56.       }
    57.     }
    58.     System.out.println(modify);
    59.   }
    60. }