题目链接:https://www.oj.swust.edu.cn/problem/show/1736
很裸的二分图,但是不知道咋回事。匈牙利跑不出解路径。没办法上了最大流。
输出解很简单,因为容量是1,所以只能满流。跑完最大流后查看残余网络,找剩余容量为0的边,输出出点和入点值就行了。
1 #include <bits/stdc++.h> 2 using namespace std; 3 4 typedef struct Edge { 5 int u, v, w, next; 6 }Edge; 7 8 const int inf = 0x7f7f7f7f; 9 const int maxn = 1111; 10 11 int cnt, dhead[maxn]; 12 int cur[maxn], dd[maxn]; 13 Edge dedge[maxn<<1]; 14 // bool vis[maxn]; // 记录经过的点 15 int S, T, N; 16 17 void init() { 18 memset(dhead, -1, sizeof(dhead)); 19 for(int i = 0; i < maxn; i++) dedge[i].next = -1; 20 S = 0; cnt = 0; 21 } 22 23 void adde(int u, int v, int w, int c1=0) { 24 dedge[cnt].u = u; dedge[cnt].v = v; dedge[cnt].w = w; 25 dedge[cnt].next = dhead[u]; dhead[u] = cnt++; 26 dedge[cnt].u = v; dedge[cnt].v = u; dedge[cnt].w = c1; 27 dedge[cnt].next = dhead[v]; dhead[v] = cnt++; 28 } 29 30 bool bfs(int s, int t, int n) { 31 // memset(vis, 0, sizeof(vis)); 32 queue<int> q; 33 for(int i = 0; i < n; i++) dd[i] = inf; 34 dd[s] = 0; 35 q.push(s); 36 while(!q.empty()) { 37 int u = q.front(); q.pop(); 38 for(int i = dhead[u]; ~i; i = dedge[i].next) { 39 if(dd[dedge[i].v] > dd[u] + 1 && dedge[i].w > 0) { 40 dd[dedge[i].v] = dd[u] + 1; 41 // vis[dedge[i].v] = 1; 42 if(dedge[i].v == t) return 1; 43 q.push(dedge[i].v); 44 } 45 } 46 } 47 return 0; 48 } 49 50 int dinic(int s, int t, int n) { 51 int st[maxn], top; 52 int u; 53 int flow = 0; 54 while(bfs(s, t, n)) { 55 for(int i = 0; i < n; i++) cur[i] = dhead[i]; 56 u = s; top = 0; 57 while(cur[s] != -1) { 58 if(u == t) { 59 int tp = inf; 60 for(int i = top - 1; i >= 0; i--) { 61 tp = min(tp, dedge[st[i]].w); 62 } 63 flow += tp; 64 for(int i = top - 1; i >= 0; i--) { 65 dedge[st[i]].w -= tp; 66 dedge[st[i] ^ 1].w += tp; 67 if(dedge[st[i]].w == 0) top = i; 68 } 69 u = dedge[st[top]].u; 70 } 71 else if(cur[u] != -1 && dedge[cur[u]].w > 0 && dd[u] + 1 == dd[dedge[cur[u]].v]) { 72 st[top++] = cur[u]; 73 u = dedge[cur[u]].v; 74 } 75 else { 76 while(u != s && cur[u] == -1) { 77 u = dedge[st[--top]].u; 78 } 79 cur[u] = dedge[cur[u]].next; 80 } 81 } 82 } 83 return flow; 84 } 85 86 int n, m; 87 88 int main() { 89 // freopen("in", "r", stdin); 90 init(); 91 int u, v; 92 scanf("%d%d",&n,&m); 93 S = 0, T = m + 1, N = T + 1; 94 for(int i = 1; i <= n; i++) adde(S, i, 1); 95 for(int i = n+1; i <= m; i++) adde(i, T, 1); 96 while(~scanf("%d%d",&u,&v)&&u+v!=-2) adde(u, v, 1); 97 printf("%d ", dinic(S, T, N)); 98 for(int i = 1; i <= n; i++) { 99 for(int j = dhead[i]; ~j; j=dedge[j].next) { 100 if(dedge[j].w == 0 && dedge[j].v != 0) printf("%d %d ", dedge[j].u, dedge[j].v); 101 } 102 } 103 return 0; 104 }