POJ 3281 Dining (最大流)
题目链接：http://poj.org/problem?id=3281
引用一下题解：http://www.cnblogs.com/kuangbin/archive/2012/08/21/2649850.html
1 #include <iostream> 2 #include <cstdio> 3 #include <cstring> 4 using namespace std; 5 const int N = 1e3 + 5; 6 const int M = 1e4 + 5; 7 const int inf = 0x3f3f3f3f; 8 struct Edge { 9 int to, next, cap, flow; 10 }edge[M]; 11 int tot, head[N], gap[N], dep[N], cur[N]; 12 void init() { 13 tot = 0; 14 memset(head, -1, sizeof(head)); 15 } 16 void addedge(int u, int v, int w, int rw = 0) { 17 edge[tot].next = head[u]; edge[tot].to = v; edge[tot].cap = w; edge[tot].flow = 0; head[u] = tot++; 18 edge[tot].next = head[v]; edge[tot].to = u; edge[tot].cap = rw; edge[tot].flow = 0; head[v] = tot++; 19 } 20 int Q[N]; 21 void bfs(int start, int end) { 22 memset(dep, -1, sizeof(dep)); 23 memset(gap, 0, sizeof(gap)); 24 gap[0] = 1; 25 int front = 0, rear = 0; 26 dep[end] = 0; 27 Q[rear++] = end; 28 while(front != rear) { 29 int u = Q[front++]; 30 for(int i = head[u]; ~i; i = edge[i].next) { 31 int v = edge[i].to; 32 if(dep[v] != -1) 33 continue; 34 Q[rear++] = v; 35 dep[v] = dep[u] + 1; 36 gap[dep[v]]++; 37 } 38 } 39 } 40 int S[N]; 41 int sap(int start, int end, int N) { 42 bfs(start, end); 43 memcpy(cur, head, sizeof(head)); 44 int top = 0; 45 int u = start; 46 int ans = 0; 47 while(dep[start] < N) { 48 if(u == end) { 49 int Min = inf; 50 int inser; 51 for(int i = 0; i < top; ++i) { 52 if(Min > edge[S[i]].cap - edge[S[i]].flow) { 53 Min = edge[S[i]].cap - edge[S[i]].flow; 54 inser = i; 55 } 56 } 57 for(int i = 0; i < top; ++i) { 58 edge[S[i]].flow += Min; 59 edge[S[i] ^ 1].flow -= Min; 60 } 61 ans += Min; 62 top = inser; 63 u = edge[S[top] ^ 1].to; 64 continue; 65 } 66 bool flag = false; 67 int v; 68 for(int i = cur[u]; ~i; i = edge[i].next) { 69 v = edge[i].to; 70 if(edge[i].cap - edge[i].flow && dep[v] + 1 == dep[u]) { 71 flag = true; 72 cur[u] = i; 73 break; 74 } 75 } 76 if(flag) { 77 S[top++] = cur[u]; 78 u = v; 79 continue; 80 } 81 int Min = N; 82 for(int i = head[u]; ~i; i = edge[i].next) { 83 if(edge[i].cap - edge[i].flow && dep[edge[i].to] < Min) { 84 Min = dep[edge[i].to]; 85 cur[u] = i; 86 } 87 } 88 gap[dep[u]]--; 89 if(!gap[dep[u]]) 90 return ans; 91 dep[u] = Min + 1; 92 gap[dep[u]]++; 93 if(u != start) 94 u = edge[S[--top] ^ 1].to; 95 } 96 return ans; 97 } 98 99 int main() 100 { 101 int n, f, d; 102 while(scanf("%d %d %d", &n, &f, &d) != EOF) { 103 int m1, m2, num; 104 init(); 105 for(int k = 1; k <= n; ++k) { 106 scanf("%d %d", &m1, &m2); 107 for(int i = 1; i <= m1; ++i) { 108 scanf("%d", &num); 109 addedge(2 * n + num, k, 1); 110 } 111 for(int i = 1; i <= m2; ++i) { 112 scanf("%d", &num); 113 addedge(n + k, 2 * n + f + num, 1); 114 } 115 } 116 for(int i = 1; i <= n; ++i) { 117 addedge(i, n + i, 1); 118 } 119 for(int i = 1; i <= f; ++i) { 120 addedge(0, 2 * n + i, 1); 121 } 122 for(int i = 1; i <= d; ++i) { 123 addedge(2 * n + f + i, 2 * n + f + d + 1, 1); 124 } 125 printf("%d\n", sap(0, 2 * n + f + d + 1, 2 * n + f + d + 2)); 126 } 127 return 0; 128 }
