UVA 12093 保衛Zonk Protecting Zonk (樹形dp)
阿新 • • 發佈:2021-07-31
題目連結:https://onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=242&page=show_problem&problem=3245
有些麻煩的樹形 \(dp\)
#include<bits/stdc++.h> using namespace std; typedef long long ll; const int maxn = 20010; int n, c1, c2; int h[maxn], cnt = 0; struct E{ int to, next; }e[maxn<<1]; void add(int u, int v){ e[++cnt].to = v; e[cnt].next = h[u]; h[u] = cnt; } int dp[maxn][2]; // 0: A 1: B int g[maxn][2]; // 不放 0: uncovered 1: covered int f[maxn]; // 兒子隨意選 0: 沒 B 1: 有 B void dfs(int u, int par){ dp[u][0] = c1, dp[u][1] = c2; g[u][0] = 0; f[u] = 0; for(int i = h[u] ; i != -1 ; i = e[i].next){ int v = e[i].to; if(v == par) continue; dfs(v, u); } int flag = 0; for(int i = h[u] ; i != -1 ; i = e[i].next){ int v = e[i].to; if(v == par) continue; if(dp[v][1] <= dp[v][0] && dp[v][1] <= g[v][0] && dp[v][1] <= g[v][1]){ flag = 1; } f[u] += min(min(dp[v][0], dp[v][1]), min(g[v][0], g[v][1])); g[u][0] += min(g[v][1], dp[v][0]); //dp[u][0] += min(min(g[v][0], g[v][1]), min(dp[v][0], dp[v][1])); dp[u][1] += min(min(min(g[v][0], g[v][1]), min(dp[v][0], dp[v][1])), f[v]); } dp[u][0] += f[u]; if(flag) { g[u][1] = min(g[u][1], f[u]); } else{ for(int i = h[u] ; i != -1 ; i = e[i].next){ int v = e[i].to; if(v == par) continue; g[u][1] = min(g[u][1], f[u] - min(min(g[v][0], g[v][1]), dp[v][0]) + dp[v][1]); } } } ll read(){ ll s = 0, f = 1; char ch = getchar(); while(ch < '0' || ch > '9'){ if(ch == '-') f = -1; ch = getchar(); } while(ch >= '0' && ch <= '9'){ s = s * 10 + ch - '0'; ch = getchar(); } return s * f; } int main(){ while(scanf("%d%d%d", &n, &c1, &c2) == 3 && n){ memset(h, -1, sizeof(h)); cnt = 0; int u, v; for(int i = 1 ; i <= n - 1 ; ++i){ scanf("%d%d", &u, &v); add(u, v); add(v, u); } memset(dp, 0x3f, sizeof(dp)); memset(f, 0x3f, sizeof(f)); memset(g, 0x3f, sizeof(g)); dfs(1, 0); printf("%d\n", min(min(g[1][0], g[1][1]), min(dp[1][1], dp[1][0]))); } return 0; }