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Floyd-Warshall algorithm finding shortest distance between all
pairs of vertices in graph. Works in O(N^3)
Based on problem 95 from
#include <iostream>
#include <fstream>
#include <cmath>
#include <algorithm>
#include <vector>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <cstdlib>
#include <cstdio>
#include <string>
#include <cstring>
#include <cassert>
#include <utility>
#include <iomanip>
using namespace std;
const int MAXN = 55;
const int INF = (int) 1e9;
int n;
int s, t;
int d[MAXN][MAXN];
int main() {
scanf("%d %d %d", &n, &s, &t);
for (int i = 1; i <= n; i++)
for (int j = 1; j <= n; j++) {
scanf("%d", &d[i][j]);
if (d[i][j] == -1)
d[i][j] = INF;
for (int k = 1; k <= n; k++)
for (int i = 1; i <= n; i++)
for (int j = 1; j <= n; j++)
if (d[i][k] + d[k][j] < d[i][j])
d[i][j] = d[i][k] + d[k][j];
if (d[s][t] == INF)
printf("%d\n", d[s][t]);
return 0;