找匹配中的关键边。
做法： 拆掉一条匹配边，然后对边两边的点做一次增广，如果可以增广，那么此边不是关键边，否则是关键边。
详情可以参见：http://www.docin.com/p-109868135.html
代码：
1 #include <iostream> 2 #include <cstdio> 3 #include <cstring> 4 #include <cstdlib> 5 #include <cmath> 6 #include <algorithm> 7 #include <string> 8 #include <queue> 9 #include <stack> 10 #include <vector> 11 #include <map> 12 #include <set> 13 #include <functional> 14 #include <time.h> 15 16 using namespace std; 17 18 const int INF = 1<<30; 19 const int MAXN = 105; 20 21 22 bool Matrix[MAXN][MAXN]; 23 int n; 24 25 int mX[MAXN], mY[MAXN], visX[MAXN], visY[MAXN]; 26 27 bool dfs(int u) { 28 visX[u] = true; 29 for (int v = 1; v <= n; v++) if (!Matrix[u][v] && !visY[v]) { 30 visY[v] = true; 31 if (mY[v]<0 || dfs(mY[v])) { 32 mY[v] = u; 33 mX[u] = v; 34 return true; 35 } 36 } 37 return false; 38 } 39 40 void input() { 41 memset(Matrix, false, sizeof(Matrix)); 42 int x, y; 43 while (scanf("%d%d", &x, &y)!=EOF && (x!=0||y!=0)) { 44 Matrix[x][y] = true; 45 } 46 } 47 48 void solve() { 49 int Max; 50 memset(mX, -1, sizeof(mX)); 51 memset(mY, -1, sizeof(mY)); 52 for (int i = 1; i <= n; i++) { 53 memset(visX, false, sizeof(visX)); 54 memset(visY, false, sizeof(visY)); 55 if (dfs(i)) Max++; 56 } 57 if (Max<n) { 58 puts("none"); 59 return ; 60 } 61 bool flag = true; 62 int delX, delY; 63 for (int i = 1; i <= n; i++) { 64 delX = i; delY = mX[i]; 65 mX[delX] = mY[delY] = -1; 66 Matrix[delX][delY] = true; 67 memset(visX, false, sizeof(visX)); 68 memset(visY, false, sizeof(visY)); 69 70 if (!dfs(i)) { 71 printf("%d %d ", delX, delY); 72 mX[delX] = delY; mY[delY] = delX; 73 flag = false; 74 } 75 Matrix[delX][delY] = false; 76 } 77 if (flag) puts("none"); 78 } 79 80 int main() { 81 #ifdef Phantom01 82 freopen("FZU1202.txt", "r", stdin); 83 #endif //Phanaom01 84 85 while (scanf("%d", &n)!=EOF) { 86 input(); 87 solve(); 88 puts(""); 89 } 90 91 return 0; 92 }