Frequently Asked Questions

Naked Freud algorithm, specified in the title, and then elaborate on the idea;

 

Freudian thought:

For n nodes, if the node acts as a relay between any other two nodes i, j, the distance between i and j can be shortened, then update;

Using three cyclic updates, the complexity is O (n ^ 3);

 

#include<iostream>
#include<vector>
#include<string>
using namespace std;

const int maxn = 210;
const int INF = 10000000;
int ma [maxn] [maxn];

int n, m;
int st, ed;

void init() {
	fill(ma[0], ma[0] + maxn * maxn, INF);
	for (int i = 0; i < n; i++) {
		has [i] [i] = 0;
	}
}

void floyd() {
	for (int k = 0; k < n; k++) {
		for (int i = 0; i < n; i++) {
			for (int j = 0; j < n; j++) {
				if (ma[i][k] != INF && ma[k][j] != INF && ma[i][k] + ma[k][j] < ma[i][j]) {
					in [i] [j] = in [i] [k] + in [k] [j];
				}
			}
		}
	}
}

int main () {
	while (cin >> n >> m) {
		init();
		int a, b, c;
		for (int i = 0; i < m; i++) {
			cin >> a >> b >> c;
			at [a] [b] = and [b] [a] = c;
		}
		cin >> st >> ed;
		floyd();
		if (ma[st][ed] == INF)
			cout << -1 << endl;
		else
			cout << ma[st][ed] << endl;
	}
}