UVA 12264 二分+最大流 基础题

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
const int maxn = 410;
const int inf = 1e9;
struct Edge {
int v, c, next;
Edge(){}
Edge(int v, int c, int next): v(v), c(c), next(next) {}
}edge[1000006];

int head[maxn], E;
int n, m;
int S, T;

void init() {
E = 0;
memset(head, -1, sizeof(head));
}
void add(int s, int t, int c) {
edge[E] = Edge(t, c, head[s]);
head[s] = E++;
edge[E] = Edge(s, 0, head[t]);
head[t] = E++;
}

int gap[maxn], dis[maxn], pre[maxn], cur[maxn];
int sap(int s, int t, int n) {
int i;
for(i = 0; i <= n; i++) {
cur[i] = head[i];
gap[i] = dis[i] = 0;
}
gap[0] = n;
int u = pre[s] = s, maxf = 0, v, aug = inf;
while(dis[s] < n) {
loop:for(i = cur[u]; ~i; i = edge[i].next) {
v = edge[i].v;
if(edge[i].c && dis[u] == dis[v]+1) {
pre[v] = u;
cur[u] = i;
aug = min(aug, edge[i].c);
u = v;
if(u == t) {
while(u != s) {
u = pre[u];
edge[cur[u]].c -= aug;
edge[cur[u]^1].c += aug;
}
maxf += aug;
aug = inf;
}
goto loop;
}
}
int d = n;
for(i = head[u]; ~i; i= edge[i].next) {
v = edge[i].v;
if(edge[i].c && dis[v] < d) {
d = dis[v];
cur[u] = i;
}
}
if(!(--gap[dis[u]])) break;
++gap[dis[u] = d+1];
u = pre[u];
}
return maxf;
}
int a[maxn];
char mp[maxn][maxn];
int sum, ans;

void build(int m) {
int i, j;
sum = 0;
init();
for(i = 0; i < n; i++)
if(a[i]) {
add(S, i, a[i]);
add(i, i+n, a[i]);
}
for(i = 0; i < n; i++) if(a[i]) {
bool g = 0;
for(j = 0; j < n; j++) if(mp[i][j] == 'Y'){
if(a[j]) add(i, j+n, inf);
else g = 1;
}
if(!g) add(i+n, T, 1), sum++;
else add(i+n, T, m), sum += m;
}
}
int main() {
int i, j, cas;
scanf("%d", &cas);
for(int ca = 1; ca <= cas; ca++) {
scanf("%d", &n);
for(i = 0; i < n; i++) scanf("%d", &a[i]);
for(i = 0; i < n; i++)
scanf("%s", mp[i]);
S = 2*n; T = S+1;
int l = 1, r = 10000;
while(l <= r) {
int mid = l+r>>1;
build(mid);
int tp = sap(S, T, T+1);
if(tp < sum) r = mid-1;
else {
ans = mid;
l = mid+1;
}
}
printf("%d\n", ans);
}
return 0;
}