2016计蒜之道复赛 百度地图的实时路况(Floyd 分治)

#include<bits/stdc++.h>
#define LL long long 
using namespace std;
const int MAXN = 301;
inline int read() {
    char c = getchar(); int x = 0, f = 1;
    while(c < '0' || c > '9') {if(c == '-') f = -1; c = getchar();}
    while(c >= '0' && c <= '9') x = x * 10 + c - '0', c = getchar();
    return x * f;
}
int N, g[MAXN][MAXN];
LL ans = 0;
void chmin(int &a, int b) {a = (a < b ? a : b);}
void solve(int l, int r) {
    if(l == r) {
        for(int i = 1; i <= N; i++) 
            for(int j = 1; j <= N; j++) 
                if(i != l && j != l) ans += (g[i][j] == 1e9 ? -1 : g[i][j]);
        return ;
    }
    int f[MAXN][MAXN];
    memcpy(f, g, sizeof(g));
    int mid = l + r >> 1;
    for(int k = mid + 1; k <= r; k++)
        for(int i = 1; i <= N; i++)
            for(int j = 1; j <= N; j++)
                if(i != k && j != k) chmin(g[i][j], g[i][k] + g[k][j]);
    solve(l, mid);
    memcpy(g, f, sizeof(g));    
    for(int k = l; k <= mid; k++) 
        for(int i = 1; i <= N; i++)
            for(int j = 1; j <= N; j++)
                if(i != k && j != k) chmin(g[i][j], g[i][k] + g[k][j]); 
    solve(mid + 1, r);
    memcpy(g, f, sizeof(g));
}
int main() {
    N = read();
    for(int i = 1; i <= N; i++)     
        for(int j = 1; j <= N; j++) {
            g[i][j] = read();
            if(g[i][j] == -1) g[i][j] = 1e9;
        }
    solve(1, N);
    cout << ans;
    return 0;
}