【CF】304 E. Soldier and Traveling

基础网络流，增加s和t，同时对于每个结点分裂为流入结点和流出结点。EK求最大流，判断最大流是否等于当前总人数。

  1 /* 304E */
  2 #include <iostream>
  3 #include <string>
  4 #include <map>
  5 #include <queue>
  6 #include <set>
  7 #include <stack>
  8 #include <vector>
  9 #include <deque>
 10 #include <algorithm>
 11 #include <cstdio>
 12 #include <cmath>
 13 #include <ctime>
 14 #include <cstring>
 15 #include <climits>
 16 #include <cctype>
 17 #include <cassert>
 18 #include <functional>
 19 using namespace std;
 20 //#pragma comment(linker,"/STACK:102400000,1024000")
 21
 22 #define rep(i, a, n)     for (int i=a;i<n;++i)
 23 #define per(i, a, n)     for (int i=n-1;i>=a;--i)
 24 #define pb                 push_back
 25 #define mp                 make_pair
 26 #define all(x)             (x).begin(),(x).end()
 27 #define SZ(x)             ((int)(x).size())
 28 #define lson            l, mid, rt<<1
 29 #define rson            mid+1, r, rt<<1|1
 30
 31 const int maxn = 205;
 32 int F[maxn][maxn];
 33 int P[maxn], a[maxn];
 34 bool visit[maxn];
 35 int ans[maxn][maxn];
 36 int ai[maxn], bi[maxn], ci[maxn];
 37 int n, m, s = 0, t;
 38 bool flag = true;
 39
 40 bool bfs() {
 41     int u, v;
 42     queue<int> Q;
 43
 44     memset(a, 0, sizeof(a));
 45     a[s] = INT_MAX;
 46     Q.push(s);
 47     P[s] = s;
 48
 49     while (!Q.empty()) {
 50         u = Q.front();
 51         Q.pop();
 52         for (v=0; v<=t; ++v) {
 53             if (!a[v] && F[u][v]) {
 54                 P[v] = u;
 55                 Q.push(v);
 56                 a[v] = min(a[u], F[u][v]);
 57             }
 58         }
 59     }
 60
 61     return a[t]==0;
 62 }
 63
 64 int Edmonds_Karp() {
 65     int u, v;
 66     int ans = 0;
 67
 68     while (1) {
 69         if (bfs())
 70             break;
 71         for (u=t,v=P[u]; u!=s; u=v, v=P[u]) {
 72             F[u][v] += a[t];
 73             F[v][u] -= a[t];
 74         }
 75         ans += a[t];
 76     }
 77     return ans;
 78 }
 79
 80 int main() {
 81     int i, j, k;
 82     int s1, s2;
 83
 84     #ifndef ONLINE_JUDGE
 85         freopen("data.in", "r", stdin);
 86         freopen("data.out", "w", stdout);
 87     #endif
 88
 89     scanf("%d %d", &n, &m);
 90     t = n+n+1;
 91     memset(F, 0, sizeof(F));
 92     memset(ans, 0, sizeof(ans));
 93     s1 = s2 = 0;
 94
 95     for (i=1; i<=n; ++i) {
 96         scanf("%d", &ai[i]);
 97         s1 += ai[i];
 98         F[0][i] = ai[i];
 99     }
100
101     for (i=1; i<=n; ++i) {
102         scanf("%d", &bi[i]);
103         s2 += bi[i];
104         F[i][i+n] = INT_MAX;
105         F[i+n][t] = bi[i];
106     }
107
108     for (i=0; i<m; ++i) {
109         scanf("%d %d", &j, &k);
110         F[j][k+n] = INT_MAX;
111         F[k][j+n] = INT_MAX;
112     }
113
114     flag = s1==s2;
115     if (flag) {
116         flag = Edmonds_Karp() == s1;
117     }
118
119     if (flag) {
120         for (i=1; i<=n; ++i)
121             for (j=n+1; j<t; ++j)
122                 ans[i][j-n] = F[j][i];
123         puts("YES");
124         for (i=1; i<=n; ++i) {
125             for (j=1; j<=n; ++j)
126                 printf("%d ", ans[i][j]);
127             putchar(‘\n‘);
128         }
129     } else {
130         puts("NO");
131     }
132
133     #ifndef ONLINE_JUDGE
134         printf("time = %d.\n", (int)clock());
135     #endif
136
137     return 0;
138 }