From 7040e27fb255985c713f70960c226b7521234700 Mon Sep 17 00:00:00 2001
From: Nidheesh Pandey <nidheeshpandey@gmail.com>
Date: Fri, 13 Oct 2017 16:07:47 +0000
Subject: [PATCH 1/3] Create Dijkstra.cpp

---
 Graph/Dijkstra.cpp | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)
 create mode 100644 Graph/Dijkstra.cpp

diff --git a/Graph/Dijkstra.cpp b/Graph/Dijkstra.cpp
new file mode 100644
index 000000000..448d4b500
--- /dev/null
+++ b/Graph/Dijkstra.cpp
@@ -0,0 +1,32 @@
+#include<bits/stdc++.h>
+using namespace std;
+vector < pair <int,int> > graph[5*100001];
+int m,n,l,x,y;
+int dis[5*100001];
+int dij(vector <pair<int,int> > * v,int s,int * dis) {
+    priority_queue < pair <int,int> , vector < pair <int,int> >,greater < pair <int,int> > > pq;
+    pq.push(make_pair(0,s));
+    dis[s] = 0;
+    int u;
+    while(!pq.empty()) {
+
+        u = (pq.top()).second;
+        pq.pop();
+        for( vector <pair <int,int> > :: iterator it = v[u].begin(); it != v[u].end();it++) {
+            if(dis[u] + it->first < dis[it->second]) {
+                dis[it->second] = dis[u] + it->first;
+                pq.push(make_pair(dis[it->second],it->second));
+            }
+        }
+    }
+}
+int main() {
+    cin>>n>>m;
+    for(int i = 0;i < m;i++) {
+        scanf("%d%d%d",&x,&y,&l);
+        graph[x].push_back(make_pair(l,y));
+        graph[y].push_back(make_pair(l,x));
+    }
+    dij(graph,1,dis);
+   
+}

From feeca868433c711cba61b6043795222478e99e5b Mon Sep 17 00:00:00 2001
From: Nidheesh Pandey <nidheeshpandey@gmail.com>
Date: Fri, 13 Oct 2017 21:25:53 +0000
Subject: [PATCH 2/3] Update Dijkstra.cpp

---
 Graph/Dijkstra.cpp | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/Graph/Dijkstra.cpp b/Graph/Dijkstra.cpp
index 448d4b500..844ad168f 100644
--- a/Graph/Dijkstra.cpp
+++ b/Graph/Dijkstra.cpp
@@ -1,5 +1,6 @@
 #include<bits/stdc++.h>
 using namespace std;
+#define INF 10000010
 vector < pair <int,int> > graph[5*100001];
 int m,n,l,x,y;
 int dis[5*100001];
@@ -27,6 +28,16 @@ int main() {
         graph[x].push_back(make_pair(l,y));
         graph[y].push_back(make_pair(l,x));
     }
-    dij(graph,1,dis);
-   
+    
+    scanf("%d",&s);
+    for(int i = 0;i < n;i++)
+        dis[i] = INF;
+    dij(graph,s,dis);
+    
+    for(int i = 0;i < n;i++)
+        if(dis[i] == INF)
+            cout<<"-1 ";
+        else
+            cout<<dis[i]<<" ";
+    return 0;
 }

From bc8ef9e8a9db3ac1db7dceff8ac7c062e26ce364 Mon Sep 17 00:00:00 2001
From: Nidheesh Pandey <nidheeshpandey@gmail.com>
Date: Thu, 28 Dec 2017 19:56:35 +0530
Subject: [PATCH 3/3] add comments and remove <bits/stdc++.h>

---
 Graph/Dijkstra.cpp | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/Graph/Dijkstra.cpp b/Graph/Dijkstra.cpp
index 844ad168f..c395cd527 100644
--- a/Graph/Dijkstra.cpp
+++ b/Graph/Dijkstra.cpp
@@ -1,16 +1,18 @@
-#include<bits/stdc++.h>
+#include <queue>
+#include <vector>
+#include <cstdio>
+#include <iostream>
 using namespace std;
 #define INF 10000010
 vector < pair <int,int> > graph[5*100001];
-int m,n,l,x,y;
 int dis[5*100001];
 int dij(vector <pair<int,int> > * v,int s,int * dis) {
     priority_queue < pair <int,int> , vector < pair <int,int> >,greater < pair <int,int> > > pq;
+    // source distance to zero.
     pq.push(make_pair(0,s));
     dis[s] = 0;
     int u;
     while(!pq.empty()) {
-
         u = (pq.top()).second;
         pq.pop();
         for( vector <pair <int,int> > :: iterator it = v[u].begin(); it != v[u].end();it++) {
@@ -22,19 +24,23 @@ int dij(vector <pair<int,int> > * v,int s,int * dis) {
     }
 }
 int main() {
+    int m,n,l,x,y,s;
+    // n--> number of nodes , m --> number of edges
     cin>>n>>m;
     for(int i = 0;i < m;i++) {
+        // input edges.
         scanf("%d%d%d",&x,&y,&l);
         graph[x].push_back(make_pair(l,y));
-        graph[y].push_back(make_pair(l,x));
+        graph[y].push_back(make_pair(l,x)); // comment this line for directed graph
     }
-    
+    // start node.
     scanf("%d",&s);
-    for(int i = 0;i < n;i++)
+    // intialise all distances to infinity.
+    for(int i = 1;i <= n;i++)
         dis[i] = INF;
     dij(graph,s,dis);
     
-    for(int i = 0;i < n;i++)
+    for(int i = 1;i <= n;i++)
         if(dis[i] == INF)
             cout<<"-1 ";
         else