# C++實現帶路徑記錄的Floyd-Warshall算法

``````#include<iostream>
#include<cctype>
#include<sstream>
#include<string>
#include<algorithm>
#include<map>
#include<cstring>
#include<cstdio>
#include<iomanip>
#include<vector>
#include<queue>

using namespace std;

const int INF = 100000000;

void ch_status(vector<vector<int> > & W, vector<vector<int> > & P, int nNodes) {
//DP, just like bellmanford.
for (int i = 0; i < nNodes; ++i) {
for (int j = 0; j < nNodes; ++j) {
if (i == j || W[i][j] == INF)
P[i][j] = -1;
else
P[i][j] = i;
}
}

for (int k = 0; k < nNodes; ++k) {
for (int i = 0; i < nNodes; ++i) {
for (int j = 0; j < nNodes; ++j) {
if (W[i][j] > W[i][k] + W[k][j]) {
W[i][j] = W[i][k] + W[k][j];
P[i][j] = P[k][j];
}
}
}
}
}

void display(const vector<vector<int> > & W) {
int nNodes = W.size();
for (int i = 0; i < nNodes; ++i) {
for (int j = 0; j < nNodes; ++j) {
cout << " " << setw(3) << W[i][j];
}
cout << endl;
}
}

int main(void) {
cout << "Floyd-Warshall algorithm for Directed Acyclic Graph: " << endl;
while (true) {

int nNodes;
cout << "Number of Nodes: ";
cin >> nNodes;

vector<vector<int> > Wgt(nNodes, vector<int>(nNodes, INF));
for (int i = 0; i < nNodes; ++i)
Wgt[i][i] = 0;

int nEdges;
cout << "Number of Edges: ";
cin >> nEdges;

cout << "Src  Dest  Dist(< " << INF << "): " << endl;
for (int i = 0; i < nEdges; ++i) {
int src, dest, dist;
cout << "[" << i << "]: ";
cin >> src >> dest >> dist;
Wgt[src][dest] = dist;
}

for (int i = 0; i < nNodes; ++i) {
for (int j = 0; j < nNodes; ++j) {
if (Wgt[i][j] != INF)
cout << " " << setw(3) << Wgt[i][j];
else
cout << " " << "INF";
}
cout << endl;
}

//O(n^3), amazing, the fastest ever known!!
vector<vector<int> > P(nNodes, vector<int>(nNodes));
while (true) {
ch_status(Wgt, P ,nNodes);
cout << "Dist:" << endl;
display(Wgt);
cout << "Pre: " << endl;
display(P);
system("pause");
}
}
return 0;
}``````