#include 
    
     using namespace std;int n, ans, c, i, j, k;bitset<2007>a[2005];int read() {    for(c = getchar(); !isdigit(c); c = getchar());    return c-'0';}int main() {    scanf("%d", &n);    for (i = 1; i <= n; a[i][i] = 1, ++i)        for (j = 1; j <= n; ++j) a[i][j] = read();    for(k = 1; k <= n; ++k)      for(i = 1; i <= n; ++i)        if (a[i][k]) a[i] |= a[k];    for(i = 1; i <= n; ++i) ans += a[i].count();    cout << ans;    return 0;}
    

注意枚举顺序

正常的floyd是 k i j枚举 k是中间点

优化的时候就不用枚举j（终点）了