[HDOJ5889]Barricade（spfa，最大流）

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=5889

求出所有最短路，标记好以后跑最大流就是最小割。

#include <bits/stdc++.h>
using namespace std;
#define fr first
#define sc second
#define cl clear
#define BUG puts("here!!!")
#define W(a) while(a--)
#define pb(a) push_back(a)
#define Rint(a) scanf("%d", &a)
#define Rll(a) scanf("%lld", &a)
#define Rs(a) scanf("%s", a)
#define Cin(a) cin >> a
#define FRead() freopen("in", "r", stdin)
#define FWrite() freopen("out", "w", stdout)
#define Rep(i, len) for(int i = 0; i < (len); i++)
#define For(i, a, len) for(int i = (a); i < (len); i++)
#define Cls(a) memset((a), 0, sizeof(a))
#define Clr(a, x) memset((a), (x), sizeof(a))
#define Full(a) memset((a), 0x7f7f7f, sizeof(a))
#define lrt rt << 1
#define rrt rt << 1 | 1
#define pi 3.14159265359
#define RT return
#define lowbit(x) x & (-x)
#define onenum(x) __builtin_popcount(x)
typedef long long LL;
typedef long double LD;
typedef unsigned long long ULL;
typedef pair<int, int> pii;
typedef pair<string, int> psi;
typedef pair<LL, LL> pll;
typedef map<string, int> msi;
typedef vector<int> vi;
typedef vector<LL> vl;
typedef vector<vl> vvl;
typedef vector<bool> vb;

const int maxn = 1100;
const int maxm = 11000;
const int inf = 1000000000;
typedef struct Edge {
  int u, v, w;
  int next;
  Edge() { next = -1; }
}Edge;

int n, m, s, t;
Edge edge[maxm];
int head[maxn], ecnt;
int d[maxn];
bool vis[maxn];
int u, v, w;

int cnt, dhead[maxn];
int cur[maxn], dd[maxn];
Edge dedge[maxm];
int S, T, N;

void adde(int u, int v, int w) {
  edge[ecnt].u = u; edge[ecnt].v = v; edge[ecnt].w = w;
  edge[ecnt].next = head[u]; head[u] = ecnt++;
}

void init() {
  Clr(head, -1); ecnt = 0; Cls(vis);
  Cls(edge);
  Clr(dhead, -1); Cls(dedge);
    cnt = 0;
}

void spfa(int s) {
  queue<int> q;
  Rep(i, n+1) d[i] = inf;
  d[s] = 0; q.push(s);
  vis[s] = 1;
  while(!q.empty()) {
    int u = q.front(); q.pop(); vis[u] = 0;
    for(int i = head[u]; ~i; i=edge[i].next) {
      int v = edge[i].v;
      if(d[v] > d[u] + 1) {
        d[v] = d[u] + 1;
        if(!vis[v]) {
          vis[v] = 1;
          q.push(v);
        }
      }
    }
  }
}

void dadde(int u, int v, int w, int c1) {
    dedge[cnt].u = u; dedge[cnt].v = v; dedge[cnt].w = w;
    dedge[cnt].next = dhead[u]; dhead[u] = cnt++;
    dedge[cnt].u = v; dedge[cnt].v = u; dedge[cnt].w = c1;
    dedge[cnt].next = dhead[v]; dhead[v] = cnt++;
}

bool bfs(int s, int t, int n) {
    queue<int> q;
    for(int i = 0; i < n; i++) dd[i] = inf;
    dd[s] = 0;
    q.push(s);
    while(!q.empty()) {
        int u = q.front(); q.pop();
        for(int i = dhead[u]; ~i; i = dedge[i].next) {
            if(dd[dedge[i].v] > dd[u] + 1 && dedge[i].w > 0) {
                dd[dedge[i].v] = dd[u] + 1;
                if(dedge[i].v == t) return 1;
                q.push(dedge[i].v);
            }
        }
    }
    return 0;
}

int dinic(int s, int t, int n) {
    int st[maxn], top;
    int u;
    int flow = 0;
    while(bfs(s, t, n)) {
        for(int i = 0; i < n; i++) cur[i] = dhead[i];
        u = s; top = 0;
        while(cur[s] != -1) {
            if(u == t) {
                int tp = inf;
                for(int i = top - 1; i >= 0; i--) {
                    tp = min(tp, dedge[st[i]].w);
                }
                flow += tp;
                for(int i = top - 1; i >= 0; i--) {
                    dedge[st[i]].w -= tp;
                    dedge[st[i] ^ 1].w += tp;
                    if(dedge[st[i]].w == 0) top = i;
                }
                u = dedge[st[top]].u;
            }
            else if(cur[u] != -1 && dedge[cur[u]].w > 0 && dd[u] + 1 == dd[dedge[cur[u]].v]) {
                st[top++] = cur[u];
                u = dedge[cur[u]].v;
            }
            else {
                while(u != s && cur[u] == -1) {
                    u = dedge[st[--top]].u;
                }
                cur[u] = dedge[cur[u]].next;
            }
        }
    }
    return flow;
}

signed main() {
  //FRead();
  int ttt;
  Rint(ttt);
  W(ttt) {
    init();
    Rint(n); Rint(m);
    Rep(i, m) {
      Rint(u); Rint(v); Rint(w);
      adde(u,v,w); adde(v,u,w);
    }
    spfa(1);
    Rep(i, ecmt) {
      if(d[edge[i].v] == d[edge[i].u] + 1) {
        dadde(edge[i].u-1, edge[i].v-1, edge[i].w, 0);
      }
    }
    S = 0; T = n - 1; N = n;
    printf("%d
", dinic(S, T, N));
  }
  RT 0;
}