输入的a和b值应在[0，n-1]的范围内。()

#include <iostream>
using namespace std;

const int maxn = 1000;
int n;
int fa[maxn], cnt[maxn];

int getRoot(int v) {
    if (fa[v] == v) return v;
    return getRoot(fa[v]);
}

int main() {
    cin >> n;
    for (int i = 0; i < n; ++i) {
        fa[i] = i;
        cnt[i] = 1;
    }
    int ans = 0;
    for (int i = 0; i < n-1; ++i) {
        int a, b, x, y;
        cin >> a >> b;
        x = getRoot(a);
        y = getRoot(b);
        ans += cnt[x] * cnt[y];
        fa[x] = y;
        cnt[y] += cnt[x];
    }
    cout << ans << endl;
    return 0;
}