ICPCCamp 2016 Day 1 - B All Pair Shortest Path (bitset)

#include <iostream>
#include <cstring>
#include <cstdio>
#include <queue>
using namespace std;

#define N 2020
#define M 200020
#define LL long long

struct bs {
#define K 40
#define B 60

LL a[K];
void reset() {
for(int i = 0; i < K; ++i) a[i] = 0;
}
void set(int k, int v) {
int t = k / B;
int p = k % B;
if(v == 1) a[t] |= 1LL << p;
else {
a[t] |= (1LL << p);
a[t] ^= 1LL << p;
}
}
bs operator & (const bs &b) const {
bs ret;
ret.reset();
for(int i = 0; i < K; ++i) {
ret.a[i] = a[i] & b.a[i];
}
return ret;
}
int lowbit() {
for(int i = 0; i < K; ++i) {
if(a[i] == 0) continue;
int ret = 0;
LL t = a[i];
while(t % 2 == 0) {
++ret;
t /= 2;
}
a[i] -= a[i] & -a[i];
return ret + i * B;
}
return 0;
}
};
bs d
;
char s
;
int n;
int dis
;
bs vis, tmp;

LL bfs(int src) {
queue<int> q;
vis.reset();
for(int i = 1; i <= n; ++i) dis[i] = n, vis.set(i, 1);
dis[src] = 0;
q.push(src);
vis.set(src, 0);
while(!q.empty()) {
int u = q.front(); q.pop();
tmp = vis & d[u];
int x;
while(x = tmp.lowbit()) {
dis[x] = dis[u] + 1;
vis.set(x, 0);
q.push(x);
}
}
LL ret = 0;
for(int i = 1; i <= n; ++i) ret += 1LL * dis[i] * dis[i];
return ret;
}

int main() {
scanf("%d", &n);
for(int i = 1; i <= n; ++i) {
d[i].reset();
scanf("%s", s + 1);
for(int j = 1; j <= n; ++j) {
d[i].set(j, s[j] - 48);
}
}
LL ans = 0;
for(int i = 1; i <= n; ++i) ans += bfs(i);
cout << ans << endl;
return 0;
}