uva 1349 - Optimal Bus Route Design（完美匹配）

题目链接：uva 1349 - Optimal Bus Route Design

权值变为负的即便为求最小值。

#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>

using namespace std;
const int maxn = 105;
const int inf = 0x3f3f3f3f;

int N, L[maxn], Lx[maxn], Ly[maxn], W[maxn][maxn], slack[maxn];
bool S[maxn], T[maxn];

int match (int u) {
S[u] = true;
for (int i = 1; i <= N; i++) if (!T[i]) {
if (Lx[u] + Ly[i] == W[u][i]) {
T[i] = true;
if (!L[i] || match(L[i])) {
L[i] = u;
return true;
}
} else
slack[i] = min(slack[i], Lx[u]+Ly[i]-W[u][i]);
}
return false;
}

void update () {
int a = inf;
for (int i = 1; i <= N; i++) if (!T[i])
a = min(a, slack[i]);

for (int i = 1; i <= N; i++) {
if (S[i]) Lx[i] -= a;
if (T[i]) Ly[i] += a;
}
}

void KM () {
for (int i = 1; i <= N; i++) {
L[i] = Lx[i] = Ly[i] = 0;
for (int j = 1; j <= N; j++)
Lx[i] = max(Lx[i], W[i][j]);
}

for (int i = 1; i <= N; i++) {
for (int j = 1; j <= N; j++) slack[j] = inf;
while (true) {
for (int j = 1; j <= N; j++) S[j] = T[j] = false;
if (match(i)) break;
else update();
}
}
}

void init () {
for (int i = 1; i <= N; i++)
for (int j = 1; j <= N; j++)
W[i][j] = -inf;
int u, v;
for (int i = 1; i <= N; i++) {
while (scanf("%d", &u) == 1 && u) {
scanf("%d", &v);
W[i][u] = max(W[i][u], -v);
}
}
}

int main () {
while (scanf("%d", &N) == 1 && N) {
init();
KM();
bool flag = false;
for (int i = 1; i <= N; i++) {
if (L[i] && W[L[i]][i] == -inf)
flag = true;
}

if (flag) printf("N\n");
else {
int ans = 0;
for (int i = 1; i <= N; i++)
ans += (Lx[i] + Ly[i]);
printf("%d\n", -ans);
}
}
return 0;
}