[代码]codeforces 274B Zero Tree

Abstract

codeforces 274B Zero Tree

树型dp

Source

http://codeforces.com/problemset/problem/274/B

Solution

艹，发现我已经快不会写代码了…赶快发个日志表示我有在做题…

Code

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

typedef long long ll;
typedef pair<ll, ll> pr;
pr (*mkpr)(ll, ll) = make_pair<ll, ll>;

int N;
ll x[111111];
ll ans = 0;
vector<int> adj[111111];

inline void nya(pr &a, pr b) {
    a.first = max(a.first, b.first);
    a.second = min(a.second, b.second);
}

void ae(int u, int v) {
    adj[u].push_back(v);
    adj[v].push_back(u);
}

pr solve(int p, int u) {
    int i, v;
    pr res = mkpr(0ll, 0ll);
    for (i = 0; i < adj[u].size(); ++i) {
        if ((v=adj[u][i])==p) continue;
        nya(res, solve(u, v));
    }
    x[u] -= res.first+res.second;
    if (x[u]>0ll) res.first += x[u];
    else res.second += x[u];
    return res;
}

int main() {
    int i, j, k;
    cin>>N;
    for (i = 1; i < N; ++i) {
        cin>>j>>k;
        ae(j, k);
    }
    for (i = 1; i <= N; ++i)
        cin>>x[i];
    pr ans = solve(0, 1);
    cout<<ans.first-ans.second<<'\n';
    return 0;
}