1 #include <algorithm> 2 #include <cstdio> 3 #include <cctype> 4 #include <queue> 5 #define INF 0x3f3f3f3f 6 #define MAXN 10010 7 #define MAXM 300010 8 using namespace std; 9 int n, m, s, t, tot = 1; 10 int beginx[MAXN], endx[MAXM], nxt[MAXM], res[MAXM]; 11 inline void add_edge(int u, int v, int w) 12 { 13 nxt[++tot] = beginx[u], beginx[u] = tot, endx[tot] = v, res[tot] = w; 14 nxt[++tot] = beginx[v], beginx[v] = tot, endx[tot] = u, res[tot] = 0; 15 } 16 struct PQ 17 { 18 int x,h; 19 PQ(int _x,int _h) 20 { 21 x = _x, h = _h; 22 } 23 bool operator < (const PQ &tar) const 24 { 25 return h < tar.h; 26 } 27 }; 28 int gap[MAXN], d[MAXN], ans[MAXN]; 29 inline bool push(int x, int y, int ptr) 30 { 31 int w = min(ans[x], res[ptr]); 32 res[ptr] -= w, res[ptr^1] += w; 33 ans[x] -= w, ans[y] += w; 34 return w; 35 } 36 inline void Gap(int val) 37 { 38 for (int i = 1; i <= n; ++i) 39 if(i != s && i != t && val < d[i] && d[i] <= n) 40 d[i] = n + 1; 41 } 42 inline int HLPP() 43 { 44 priority_queue<PQ> pq; 45 d[s] = n, ans[s] = INF, pq.push(PQ(s, d[s])); 46 int u; 47 while(!pq.empty()) 48 { 49 u = pq.top().x, pq.pop(); 50 if(!ans[u]) continue; 51 for(int i = beginx[u], v = endx[i]; i; i = nxt[i], v = endx[i]) 52 if((u == s || d[u] == d[v] + 1) && push(u, v, i) && v != t && v != s) 53 pq.push(PQ(v, d[v])); 54 if (u != s && u != t && ans[u]) 55 { 56 if(!(--gap[d[u]])) Gap(d[u]); 57 ++gap[++d[u]]; 58 pq.push(PQ(u, d[u])); 59 } 60 } 61 return ans[t]; 62 } 63 int main() 64 { 65 scanf("%d%d%d%d",&n,&m,&s,&t); 66 for(int i = 1; i <= m; i++) 67 { 68 int u,v,r; 69 scanf("%d%d%d",&u,&v,&r); 70 add_edge(u, v, r); 71 } 72 printf("%d", HLPP()); 73 return 0; 74 }
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