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  • HDU6201 transaction transaction transaction

    树形dp

    dp[i][0]表示从i点及其子树中买入的最大收益(负数)

    dp[i][1]表示从i点及其子树中卖出的最大收益(正数)

    #include <bits/stdc++.h>
    #define INF 0x3f3f3f3f
    #define full(a, b) memset(a, b, sizeof a)
    #define FAST_IO ios::sync_with_stdio(false), cin.tie(0), cout.tie(0)
    using namespace std;
    typedef long long ll;
    inline int lowbit(int x){ return x & (-x); }
    inline int read(){
        int ret = 0, w = 0; char ch = 0;
        while(!isdigit(ch)) { w |= ch == '-'; ch = getchar(); }
        while(isdigit(ch)) ret = (ret << 3) + (ret << 1) + (ch ^ 48), ch = getchar();
        return w ? -ret : ret;
    }
    inline int gcd(int a, int b){ return b ? gcd(b, a % b) : a; }
    inline int lcm(int a, int b){ return a / gcd(a, b) * b; }
    template <typename T>
    inline T max(T x, T y, T z){ return max(max(x, y), z); }
    template <typename T>
    inline T min(T x, T y, T z){ return min(min(x, y), z); }
    template <typename A, typename B, typename C>
    inline A fpow(A x, B p, C lyd){
        A ans = 1;
        for(; p; p >>= 1, x = 1LL * x * x % lyd)if(p & 1)ans = 1LL * x * ans % lyd;
        return ans;
    }
    const int N = 100005;
    int _, n, w[N], head[N], cnt, dp[N][2], ans;
    struct Edge { int v, next, w; } edge[N<<1];
    
    void build(){
        cnt = 0, ans = -INF;
        full(head, -1), full(w, 0);
    }
    
    void addEdge(int a, int b, int c){
        edge[cnt].v = b, edge[cnt].next = head[a], edge[cnt].w = c, head[a] = cnt ++;
    }
    
    void dfs(int s, int fa){
        dp[s][0] = -w[s], dp[s][1] = w[s];
        for(int i = head[s]; i != -1; i = edge[i].next){
            int u = edge[i].v;
            if(u == fa) continue;
            dfs(u, s);
            dp[s][0] = max(dp[s][0], dp[u][0] - edge[i].w);
            dp[s][1] = max(dp[s][1], dp[u][1] - edge[i].w);
        }
        ans = max(ans, dp[s][0] + dp[s][1]);
    }
    
    int main(){
    
        for(_ = read(); _; _ --){
            build();
            n = read();
            for(int i = 1; i <= n; i ++) w[i] = read();
            for(int i = 0; i < n - 1; i ++){
                int u = read(), v = read(), c = read();
                addEdge(u, v, c), addEdge(v, u, c);
            }
            dfs(1, 0);
            printf("%d
    ", ans);
        }
        return 0;
    }
    
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  • 原文地址:https://www.cnblogs.com/onionQAQ/p/11197498.html
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