网络流问题 ISAP邻接表形式
const int MAXN = 100010; //点数的最大值
const int MAXM = 400010; //边数的最大值
const int INF = 0x3f3f3f3f;
struct Edge {
int to, next, cap, flow;
} edge[MAXM]; //注意是MAXM
int tol;
int head[MAXN];
int gap[MAXN], dep[MAXN], pre[MAXN], cur[MAXN];
void init() {
tol = 0;
memset(head, -1, sizeof(head));
}
//加边,单向图三个参数,双向图四个参数
void addedge(int u, int v, int w, int rw = 0) {
edge[tol].to = v;
edge[tol].cap = w;
edge[tol].next = head[u];
edge[tol].flow = 0;
head[u] = tol++;
edge[tol].to = u;
edge[tol].cap = rw;
edge[tol].next = head[v];
edge[tol].flow = 0;
head[v] = tol++;
}
//输入参数:起点、终点、点的总数
//点的编号没有影响,只要输入点的总数
int sap(int start, int end, int N) {
memset(gap, 0, sizeof(gap));
memset(dep, 0, sizeof(dep));
memcpy(cur, head, sizeof(head));
int u = start;
pre[u] = -1;
gap[0] = N;
int ans = 0;
while (dep[start] < N) {
if (u == end) {
int Min = INF;
for (int i = pre[u]; i != -1; i = pre[edge[i ^ 1].to])
if (Min > edge[i].cap - edge[i].flow)
Min = edge[i].cap - edge[i].flow;
for (int i = pre[u]; i != -1; i = pre[edge[i ^ 1].to]) {
edge[i].flow += Min;
edge[i ^ 1].flow -= Min;
}
u = start;
ans += Min;
continue;
}
bool flag = false;
int v;
for (int i = cur[u]; i != -1; i = edge[i].next) {
v = edge[i].to;
if (edge[i].cap - edge[i].flow && dep[v] + 1 == dep[u]) {
flag = true;
cur[u] = pre[v] = i;
break;
}
}
if (flag) {
u = v;
continue;
}
int Min = N;
for (int i = head[u]; i != -1; i = edge[i].next)
if (edge[i].cap - edge[i].flow && dep[edge[i].to] < Min) {
Min = dep[edge[i].to];
cur[u] = i;
}
gap[dep[u]]--;
if (!gap[dep[u]])
return ans;
dep[u] = Min + 1;
gap[dep[u]]++;
if (u != start)
u = edge[pre[u] ^ 1].to;
}
return ans;
}