hdu 5483 Nux Walpurgis(最小生成树+dfs)

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题目链接：hdu 5483 Nux Walpurgis

解题思路

先求一下最小生成树。然后枚举起点，遍历整棵树，维护树边能被替换的最小权值。

代码

#pragma comment(linker, "/STACK:102400000,102400000")#include <cstdio>#include <cstring>#include <vector>#include <algorithm>using namespace std;const int maxn = 3005;const int inf = 0x3f3f3f3f;struct Edge {    int u, v, w;    Edge(int u = 0, int v = 0, int w = 0): u(u), v(v), w(w) {}    bool operator < (const Edge& a) const { return w < a.w; }};int N, F[maxn], W[maxn], T[maxn];int E, first[maxn], jump[maxn<<1], linker[maxn<<1], idx[maxn<<1];vector<Edge> S;vector<int> D[maxn];void addEdge(int u, int v, int w) {    jump[E] = first[u];    linker[E] = v;    idx[E] = w;    first[u] = E++;}int find (int x) { return x == F[x] ? x : F[x] = find(F[x]); }void set(int u, int v, int w) {    if (u > v) swap(u, v);    D[u][v-u-1] = w;}int get (int u, int v) {    if (u > v) swap(u, v);    return D[u][v-u-1];}void init () {    S.clear();    scanf("%d", &N);    int x;    for (int i = 0; i < N; i++) {        D[i].clear();        for (int j = 1; j < N-i; j++) {            scanf("%d", &x);            D[i].push_back(x);            S.push_back(Edge(i, i+j, x));        }    }}void miniTree () {    E = 0;    memset(first, -1, sizeof(first));    for (int i = 0; i < N; i++) F[i] = i;    int n = N;    sort(S.begin(), S.end());    for (int i = 0; i < S.size(); i++) {        int u = S[i].u, v = S[i].v;        if (find(u) != find(v)) {            F[find(u)] = find(v);            addEdge(u, v, n);            addEdge(v, u, n);            set(u, v, inf);            W[n--] = S[i].w;            if (n == 1) break;        }    }}int dfs (int u, int fa, int rt, int id, int w) {//  printf("rt=%d fa=%d u=%d %d %d\n", rt, fa, u, id, w);    for (int i = first[u]; i + 1; i = jump[i]) {        int v = linker[i];        if (v == fa) continue;        w = min(w, dfs(v, u, rt, idx[i], get(rt, v)));    }    T[id] = min(T[id], w);    return w;}int main () {    int cas;    scanf("%d", &cas);    while (cas--) {        init();        miniTree();        for (int i = 1; i <= N; i++) T[i] = inf;        for (int i = 0; i < N; i++) dfs(i, i, i, 1, inf);        int ans = 0;        for (int i = 2; i <= N; i++) {            if (T[i] != W[i]) ans++;        }        printf("%d\n", ans);    }    return 0;}

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