隊友給了一道題，不知道哪兒的，沒法驗題，先寫一版代碼占個坑，回頭驗了再改

#include<iostream> #include<algorithm> #include<stdio.h> #include<string> #include<string.h> #include<math.h> #define PI acos(-1) #define max(a, b) a > b ? a : b #define min(a, b) a < b ? a : b #define ios ios::sync_with_stdio(false) #define endl '\n' #define memset(a,b) memset(a, b, sizeof a) #define forr(i, l, r) for(int i = l; i <= r; i++) #pragma GCC optimize(2) typedef long long ll; typedef long double ld;using namespace std;const int N = 2e5 + 7; int n; int to[2 * N], nexto[2 * N], head[N], idx;void add(int a, int b) {to[idx] = b, nexto[idx] = head[a], head[a] = idx++;to[idx] = a, nexto[idx] = head[b], head[b] = idx++; }int dfs(int g, int d, int f) {if (nexto[head[g]] == -1 && to[head[g]] == f)return d;int res = d;for (int i = head[g]; ~i; i = nexto[i]) {int t = to[i];if (t != f)res += dfs(t, 1 - d, g);}return res; }int ans, js[2]; void writ(int g, int f, int d) {int k = 0;for (int i = head[g]; ~i; i = nexto[i]) {k++;int t = to[i];if (t != f) writ(t, g, 1 - d);}ans += js[d] - k; }int main() {ios;memset(head, -1);cin >> n;forr (i, 2, n) {int a, b;cin >> a >> b;add(a, b);}js[0] = dfs(1, 0, 0), js[1] = n - js[0];writ(1, 0, 0);cout << ans / 2 << endl;return 0; }

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