codeforces 812E Sagheer and Apple Tree

codeforces 812E Sagheer and Apple Tree

题意

题解

代码

#include<bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define rep(i, a, b) for(int i=(a); i<(b); i++)
#define sz(a) (int)a.size()
#define de(a) cout << #a << " = " << a << endl
#define dd(a) cout << #a << " = " << a << " "
#define all(a) a.begin(), a.end()
#define endl "\n"
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
//---

const int N = 101010, M = N*100;

int n;
int a[N], cnt[2][M], dep[N];
vi g[N];

void dfs(int u, int fa) {
    dep[u] = dep[fa] ^ 1;
    ++cnt[dep[u]][a[u]];
    for(auto v : g[u]) dfs(v, u);
}

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(0);
    ///
    cin >> n;
    ///read
    rep(i, 1, n+1) cin >> a[i];
    rep(v, 2, n+1) {
        int u;
        cin >> u;
        g[u].pb(v);
    }
    ///solve
    dfs(1, 0);
    ll ans = 0;
    int sum = 0, res = 0, c;
    rep(i, 1, n+1) if(sz(g[i])==0) {
        c = dep[i];
        break;
    }
    rep(i, 1, n+1) if(dep[i]==c) sum ^= a[i], ++res;
    if(sum) {
        rep(i, 1, n+1) if(dep[i]==c) {
            int t = sum ^ a[i];
            if(t<M) ans += cnt[c^1][t];
        }
    } else {
        ans = 1ll*res*(res-1)/2;
        res = n - res;
        ans += 1ll*res*(res-1)/2;
        rep(i, 1, M) ans += 1ll*cnt[0][i]*cnt[1][i];
    }
    cout << ans << endl;
    return 0;
}