PAT1118. Birds in Forest （并查集）

思路：并查集一套带走。

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AC代码

#include <stdio.h>
#include <string.h>
#include <algorithm>
using namespace std;
const int maxn = 10000+5;

int par[maxn], vis[maxn];

int findRoot(int x) {
    return x == par[x] ? x : par[x] = findRoot(par[x]);
}

void unionSet(int x, int y) {
    x = findRoot(x);
    y = findRoot(y);
    if(x != y) {
        par[x] = y;
    }
}

void init(int n) {
    memset(vis, 0, sizeof(vis));
    for(int i = 0; i <= n; i++) {
        par[i] = i;
    }
}

int main() {
    int n, k, q, len;
    len = -1;
    scanf("%d", &n);
    init(maxn);
    for(int i = 0; i < n; i++) {
        int x, y;
        scanf("%d%d", &k, &x);
        len = max(len, x);
        for(int j = 1; j < k; j++) {
            scanf("%d", &y);
            len = max(len, y);
            unionSet(x, y);
            x = y;
        }
    }
    int tol = 0;
    for(int i = 1; i <= len; i++) {
        int root = findRoot(i);
        if(!vis[root]) {
            vis[root] = 1;
            tol++;
        }
    }
    printf("%d %d\n", tol, len);
    scanf("%d", &q);
    int x, y;
    for(int i = 0; i < q; i++) {
        scanf("%d%d", &x, &y);
        x = findRoot(x);
        y = findRoot(y);
        if(x == y) {
            printf("Yes\n");
        } else {
            printf("No\n");
        }
    }
    return 0;
}

如有不当之处欢迎指出！