Module: Floyd's algorithm


Problem

1/10

Floyd: The Beginning (C++)

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Problem

Given a directed graph whose edges are assigned some non-negative weights (lengths). Find the length of the shortest path from vertex s to vertex t.
 
Input
The first line contains three numbers: the number of vertices in the graph N ≤50, the numbers of vertices s and t. Next comes the adjacency matrix of the graph, that is, N rows, each of which contains N numbers. The j-th number in the i-th row of the adjacency matrix specifies the length of the edge leading from the i-th vertex to the j-th one. Lengths can take any value from 0 to 1000000, the number -1 means that there is no corresponding edge. It is guaranteed that there are zeros on the main diagonal of the matrix.
 
Output
Print a single number – minimum path length. If the path does not exist, print -1.

Examples
# Input Output
1
3 1 2
0 -1 3
7 0 1
2 215 0
 218

time 1000 ms
memory 32 Mb
Rules for program design and list of errors in automatic problem checking

Teacher commentary

Insert the missing code snippets
C++
Write the program below 
#include <vector>
#include <iostream>
#include <climits>
using namespace std;

const int inf = INT_MAX;

int main()
{
	int n, s, t;
	cin >> n >> s >> t;
	vector<vector<int> > d(n + 1, vector<int>(n + 1,inf));
	for (int i = 0; i < n; ++i)
	{
		for (int j = 0; j < n; ++j)
		{
			int a;
			cin >> a;
			if (a != -1)
			{
				d[i + 1][j + 1] = a;
			}
		}
	}
	for (int k = 1; k <= n; ++k)
	{
		for (int i = 1; i <= n; ++i)
		{
			for (int j = 1; j <= n; ++j)
			{    
			}
		}
	}
	if (d[s][t] == inf)
	{
		cout << -1;
		return 0;
	}
	cout << d[s][t] << endl;

}

     

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