hdu 4679 Terrorist’s destroy（树形dp）

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题目链接：hdu 4679 Terrorist’s destroy
代码

#pragma comment(linker, "/STACK:102400000,102400000")#include <cstdio>#include <cstring>#include <queue>#include <vector>#include <algorithm>using namespace std;typedef pair<int,int> pii;const int maxn = 100005;const int inf = 0x3f3f3f3f;int N, W[maxn], L[maxn], R[maxn], D[maxn];vector<pii> G[maxn];void init () {    scanf("%d", &N);    for (int i = 1; i <= N; i++) G[i].clear();    int u, v;    for (int i = 1; i < N; i++) {        scanf("%d%d%d", &u, &v, &W[i]);        G[u].push_back(make_pair(v, i));        G[v].push_back(make_pair(u, i));        L[i] = R[i] = -inf;    }}int solve(int& s, int& e) {    memset(D, inf, sizeof(D));    D[1] = 0;    queue<int> que;    que.push(1);    while (!que.empty()) {        s = que.front();        que.pop();        for (int i = 0; i < G[s].size(); i++) {            int v = G[s][i].first;            if (D[v] > D[s] + 1) {                D[v] = D[s] + 1;                que.push(v);            }        }    }    memset(D, inf, sizeof(D));    D[s] = 0;    que.push(s);    while (!que.empty()) {        e = que.front();        que.pop();        for (int i = 0; i < G[e].size(); i++) {            int v = G[e][i].first;            if (D[v] > D[e] + 1) {                D[v] = D[e] + 1;                que.push(v);            }        }    }    return D[e];}int dep[maxn], son[maxn], len[maxn], idx[maxn];void dfs(int u, int f) {    dep[u] = dep[f] + 1;    son[u] = 0;    len[u] = dep[u];    for (int i = 0; i < G[u].size(); i++) {        int v = G[u][i].first;        if (v == f) continue;        dfs(v, u);        if (len[v] > len[u]) {            son[u] = v;            idx[u] = G[u][i].second;            len[u] = len[v];        }    }    //printf("%d %d %d\n", u, son[u], idx[u]);}void dfs(int u, int f, int deter, int id, int* a) {    if (u == 0) return;    a[id] = max(a[id], deter);    int k = dep[u];    for (int i = 0; i < G[u].size(); i++) {        int v = G[u][i].first;        if (v == f || v == son[u]) continue;        k = max(k, dep[v]);    }    dfs(son[u], u, max(deter, k), idx[u], a);}int main () {    int cas;    scanf("%d", &cas);    for (int kcas = 1; kcas <= cas; kcas++) {        init();        int s, e;        int deter = solve(s, e);        dep[0] = -1;        dfs(s, 0);        dfs(s, 0, 0, 0, L);        dep[0] = -1;        dfs(e, 0);        dfs(e, 0, 0, 0, R);        int ans = inf, id = 0, x;        for (int i = 1; i < N; i++) {            if (L[i] < 0 || R[i] < 0) x = deter;            else x = max(L[i], R[i]);            if (x * W[i] < ans) {                ans = x * W[i];                id = i;            }        }        printf("Case #%d: %d\n", kcas, id);    }    return 0;}
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