Merge pull request matthewsamuel95#809 from some1specialnew/patch-1

Create Diameter of tree

Author: matthewsamuel95

Graph/Diameter_of_tree/Diameter_of_tree.cpp

@@ -0,0 +1,85 @@
+#include <bits/stdc++.h>
+using namespace std;
+ 
+#define INF 0x3f3f3f3f
+#define MOD 1000000007
+
+#define ll long long
+#define pb push_back
+#define nl printf("\n");
+#define vint vector<int>
+
+vector<pair<int,int>>g[100005];
+int n;
+int dist[100005];
+void shortest_path(int s)
+{
+	for(int i=0;i<100001;i++)
+		dist[i]=INF;
+	set<pair<int,int>> setds;
+
+	setds.insert({0,s});
+	dist[s]=0;
+	while(!setds.empty())
+	{
+		pair<int,int> temp;
+		temp=*(setds.begin());
+		setds.erase(setds.begin());
+
+		int u=temp.second;
+		vector<pair<int,int>>::iterator it;
+		for(it=g[u].begin();it!=g[u].end();it++)
+		{
+			int v = (*it).first;
+			int weight = (*it).second;
+			if(dist[v] > dist[u] + weight)
+			{
+				if(dist[v] != INF)
+					setds.erase(setds.find({dist[v],v}));
+
+				dist[v]=dist[u] + weight;
+				setds.insert({dist[v],v});
+			}
+		}
+	}
+
+	// printf("Vertex   Distance from Source\n");
+ //    for (int i = 0; i <= n ; ++i)
+ //        printf("%d \t\t %d\n", i, dist[i]);
+
+}
+
+int main()
+{
+    ifstream myFile("task.in");
+    if(!myFile.fail())
+    {
+        assert(freopen("task.in", "r", stdin));
+    }
+    int m;
+	cin>>n>>m;
+	n--;				//starting from 0
+    int total=0;
+    for(int i=0;i<m;i++)
+    {
+    	int x,y,w;
+    	cin>>x>>y>>w;
+    	g[x].pb({y,w});
+    	g[y].pb({x,w});
+    	total+=w;
+    }
+    shortest_path(0);
+    int ma=0,ind; 
+    for(int i=0;i<n;i++)
+   		if(dist[i] > ma) 
+   			ind=i,ma=dist[i];
+   	for(int i=0;100001;i++)
+   		dist[i]=INF;
+   	shortest_path(ind);
+   	for(int i=0;i<n;i++)
+   		if(dist[i] > ma) 
+   			ind=i,ma=dist[i];
+   	cout<<(total - dist[ind]);
+   	nl
+	return 0;
+}