3396: [Usaco2009 Jan]Total flow 水流 (最大流)

#include<iostream>
#include<cstring>
#include<cstdio>
#define inf 0x7fffffff
using namespace std;

inline int read() {
int x = 0, f = 1;
char ch = getchar();
while (ch < '0' || ch > '9') {
if (ch == '-')f = -1;
ch = getchar();
}
while (ch >= '0' && ch <= '9') {
x = x * 10 + ch - '0';
ch = getchar();
}
return x*f;
}

struct edge {
int to, next, v;
} e[50001];
int n, cnt = 1, ans, T = 801, head[50001], h[50001];

void insert(int u, int v, int w) {
e[++cnt] = (edge){v, head[u], w};
head[u] = cnt;
e[++cnt] = (edge){u, head[v], 0};
head[v] = cnt;
}

inline bool bfs() {
int q[50001], t = 0, w = 0;
memset(h, -1, sizeof (h));
h[0] = 0;
while (t <= w) {
int now = q[t++];
for (int i = head[now]; i; i = e[i].next) {
if (e[i].v && h[e[i].to] == -1) {
h[e[i].to] = h[now] + 1;
q[++w] = e[i].to;
}
}
}
if (h[T] == -1)return 0;
else return 1;
}

inline int dfs(int x, int f) {
if (x == T)return f;
int rest, used = 0;
for (int i = head[x]; i; i = e[i].next) {
if (e[i].v && h[e[i].to] == h[x] + 1) {
rest = f - used;
rest = dfs(e[i].to, min(e[i].v, rest));
e[i].v -= rest;
e[i ^ 1].v += rest;
used += rest;
if (used == f)return f;
}
}
if (!used)h[x] = -1;
return used;
}

void dinic() {
while (bfs())ans += dfs(0, inf);
}

int main() {
n = read();
for (int i = 1; i <= n; i++) {
char ch[2];
int a, b, c;
scanf("%s", ch);
a = ch[0] - 'A' + 1;
scanf("%s", ch);
b = ch[0] - 'A' + 1;
c = read();
insert(a, b, c);
}
insert(0, 1, inf);
insert(26, T, inf);
dinic();
printf("%d", ans);
return 0;
}