Tenka1 Programmer Contest 2019 E

题目链接

参考博客

关于check()函数，相隔p-1取出来，提出一个公因数后，剩下的为(x^{p-1},x^{2*(p-1)}…x^{n*(p-1)})，x与p互质，各项的幂取余p的欧拉函数为0。

#include "bits/stdc++.h"
 
using namespace std;
typedef long long ll;
const int mod = 1e9 + 7;
const int maxn = 1e6 + 100;
const int inf = 0x3f3f3f3f;
 
vector<pair<int, int> > e[maxn];
 
int n, k;
int vis[maxn];
int xorr[maxn];
 
void read(int &x) {
    x = 0;
    char ch, c = getchar();
    while (c < '0' || c > '9') ch = c, c = getchar();
    while (c >= '0' && c <= '9') x = x * 10 + c - '0', c = getchar();
    if (ch == '-') x = -x;
}
 
void dfs(int now) {
    if (vis[now]) return;
    vis[now] = 1;
    for (auto x:e[now]) {
        if (!vis[x.first]) {
            xorr[x.first] = xorr[now] ^ x.second;
            dfs(x.first);
        }
    }
}
 
unordered_map<int, int> mp;
 
int main() {
   // freopen("in.txt", "r", stdin);
    read(n);
    read(k);
    int x, y, z;
    for (int i = 1; i < n; i++) {
        read(x);
        read(y);
        read(z);
        e[x].push_back({y, z});
        e[y].push_back({x, z});
    }
    dfs(1);
    for (int i = 1; i <= n; i++) {
        mp[xorr[i]]++;
    }
    ll ans = 0;
    for (int i = 1; i <= n; i++) {
        mp[xorr[i]]--;
        x = xorr[i] ^ k;
        ans += mp[x];
        mp[xorr[i]]++;
    }
    cout << ans / 2 << endl;
    return 0;
}