网络流sap需要注意的地方

int sap(){memset(level, 0, sizeof level);memset(gap, 0, sizeof gap);memset(cur, 0, sizeof cur);int u = pre[s] = s;int aug = inf;gap[s] = n;这个要使源点gap值为点个数int v;int flow = 0;while(level[s] < n){for(v = cur[u]; v < n; v ++){if(c[u][v] > 0 && level[u] == level[v] + 1){break;}}if(v < n){pre[v] = u;if(aug > c[u][v]) aug = c[u][v];u = cur[u] = v;if(u == t){flow += aug;for(v = t; v != s; v = pre[v]){if(c[pre[v]][v] != inf)c[pre[v]][v] -= aug;if(c[v][pre[v]] != inf)c[v][pre[v]] += aug;}aug = inf, u = s;}}else{int min_label = t;这个要从t开始，因为如果都不满足的话min_label就是t了，也就是最大for(v = 0; v < n; v ++){if(c[u][v] > 0 && min_label > level[v]){cur[u] = v;min_label = level[v];}}if(--gap[level[u]] == 0) return flow;level[u] = min_label + 1;gap[level[u]] ++;u = pre[u];}}return flow;
}