HDU6026 Deleting Edges （最短路树计数）

题意：

分析：

代码：

#define inf 0x3f3f3f3f
#define mod 1000000007
#define maxn 55
int w[maxn][maxn], d[maxn], n, v[maxn];
void dijk(int st) {
memset(d, 0x3f, sizeof d);
memset(v, 0, sizeof v);
d[st] = 0;
for (int i = 0; i < n; i++) {
int m = inf, tmp = -1;
for (int j = 0; j < n; j++) {
if (!v[j] && m > d[j]) {
m = d[tmp = j];
}
}
if (tmp == -1) {
break;
}
v[tmp] = 1;
for (int j = 0; j < n; j++) {
if (!v[j] && d[j] > d[tmp] + w[tmp][j]) {
d[j] = d[tmp] + w[tmp][j];
}
}
}
}
char a[maxn];
int c[maxn];
int cmp(int i, int j) {
return d[i] < d[j];
}
int main()
{
while (~scanf("%d", &n)) {
for (int i = 0; i < n; i++) {
scanf("%s", a);
for (int j = 0; j < n; j++) {
w[i][j] = a[j] - '0';
if (w[i][j] == 0) {
w[i][j] = inf;
}
}
c[i] = i;
}
dijk(0);
sort(c, c + n, cmp);
ll ans = 1;
for (int i = 1; i < n; i++) {
ll p  = 0;
for (int j = 0; j < i; j++) {
if (d[c[i]] == d[c[j]] + w[c[i]][c[j]]) {
p++;
}
}
ans = ans * p % mod;
}
printf("%lld\n", ans);
}
}