[英]Floyd-Warshall algorithm implementation not working
我正在為分配執行Floyd-Warshall算法,並且輸出矩陣不正確。 我已經在線對其他算法仔細檢查了算法,它看起來和其他算法一樣。 我只是想念什么嗎? 任何幫助表示贊賞。
我的輸入文件是:
4
0 2 2 -1
-1 0 2 3
-1 -1 0 2
-1 -1 -1 0
結果矩陣應為:
0 2 2 4
-1 0 2 3
-1 -1 0 2
-1 -1 -1 0
路徑矩陣應為:
0 0 0 3
0 0 0 0
0 0 0 0
0 0 0 0
我收到的結果矩陣是:
-4 -3 -2 -5
-5 -4 -3 -6
-6 -5 -4 -7
-7 -6 -5 -8
對於路徑矩陣:
4 4 4 4
4 4 4 4
4 4 4 4
4 4 4 4
這是我的程序的代碼 :
#include <iostream>
#include <fstream>
#include <vector>
#include <string>
#include <iomanip>
using namespace std;
// Forward Declarations
void readFile();
void fillPathWithZeros();
void findFloydsAlgorithmMatrix();
void printGraph(vector< vector<int> >& inVector, string heading);
int size;
vector< vector<int> > M; // Matrix with weights
vector< vector<int> > P; // Path Matrix
int main()
{
readFile();
fillPathWithZeros();
findFloydsAlgorithmMatrix();
cin.get();
return 0;
}
void readFile()
{
int z = 0;
ifstream file("example.txt", fstream::in); // File name is example.txt
if (file.is_open())
{
// read characters by using "file >>"
file >> z;
size = z;
vector< vector<int> > fileGraph(size, vector<int>(size)); // creates a local 2D vector to size stated in file
for (int i = 0; i < size; i++)
{
for (int j = 0; j < size; j++)
{
file >> fileGraph[i][j];
}
}
M = fileGraph; // Copies the local vector to a global vector to be used in other functions
printGraph(fileGraph, "Input matrix M: "); // Print out the input Matrix
}
}
// Initialize the Path Vector with all 0's
void fillPathWithZeros()
{
vector< vector<int> > localPathGraph(size, vector<int>(size));
for (int i = 0; i < size; i++){
for (int j = 0; j < size; j++) {
localPathGraph[i][j] = 0;
}
}
P = localPathGraph; // set the local Path Vector to the Global Path Vector
}
void findFloydsAlgorithmMatrix()
{
for (int k = 0; k < size; k++) {
for (int i = 0; i < size; i++) {
for (int j = 0; j < size; j++){
if ( ( M[i][k] + M[k][j] ) < M[i][j] ) {
M[i][j] = M[i][k] + M[k][j];
P[i][j] = k + 1;
}
}
}
}
printGraph(M, "Resultant matrix M: ");
printGraph(P, "Path matrix P: ");
}
void printGraph(vector< vector<int> >& inVector, string heading){
cout << heading << endl;
for (int i = 0; i < size; i++){
for (int j = 0; j < size; j++) {
cout << setw(2) << inVector[i][j] << " ";
}
cout << endl;
}
cout << endl;
}
矩陣中存在負距離。 Floyd-Warshall不適用於負距離或負循環。
參見此處: http : //en.wikipedia.org/wiki/Floyd%E2%80%93Warshall_algorithm
就您的代碼而言,從算法角度來看似乎還可以。 有些事情可以用較短的代碼來完成(例如向量的初始化),但除此之外,如果矩陣沒有負距離/周期,則代碼應該可以工作。
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