Merge pull request #2 from TheSYNcoder/master

leetcode problems added

README.md

@@ -18,6 +18,7 @@ A repository containing link of good interview questions.
 * [Reducing Dishes](https://leetcode.com/problems/reducing-dishes/),[Solution](https://github.com/TheSYNcoder/InterviewPrep/blob/master/Solutions/reducing-dishes.cpp)
 * [K-different subarrays](https://leetcode.com/articles/subarrays-with-k-different-integers/)
 * [Possible Bipartition](https://leetcode.com/problems/possible-bipartition/) , [Solution](https://github.com/TheSYNcoder/InterviewPrep/blob/master/Solutions/Possible%20Bipartition.cpp)
+* [Course Schedule](https://leetcode.com/explore/challenge/card/may-leetcoding-challenge/538/week-5-may-29th-may-31st/3344/), [Solution](https://github.com/TheSYNcoder/InterviewPrep/blob/master/Solutions/Course_Schedule.cpp)
 * [Distinct Subsequences](https://leetcode.com/problems/distinct-subsequences-ii/)
 * [Minimum Cost for Tickets [DP] ](https://leetcode.com/problems/minimum-cost-for-tickets/)
 * [Valid perfect square [Bin Search]](https://leetcode.com/problems/valid-perfect-square/). [Solution](Solutions/is_perfect_square.cpp) (Little tricky implementation)

Solutions/Course_Schedule.cpp

@@ -0,0 +1,40 @@
+#include<bits/stdc++.h>
+using namespace std;
+
+//The solution basically uses the concept of graph coloring
+// 0: node has not been visited
+// 2: node is in processing mode
+// 1: node has allready been processed
+
+class Solution {
+private:
+    bool isCyclic(vector<vector<int>>&adj,vector<int>&visited,int current){
+        if(visited[current]==2)
+            return true;
+        visited[current]=2;
+        for(int i=0;i<adj[current].size();i++){
+            if(visited[adj[current][i]]!=1){
+                if(isCyclic(adj,visited,adj[current][i]))
+                    return true;
+            }
+        }
+        visited[current]=1;
+        return false;
+    }
+public:
+    bool canFinish(int numCourses, vector<vector<int>>& prerequisites) {
+        vector<vector<int>>adj(numCourses);
+        for(int i=0;i<prerequisites.size();i++){
+            adj[prerequisites[i][0]].push_back(prerequisites[i][1]);
+        }
+        vector<int>visited(numCourses,0);
+        for(int i=0;i<numCourses;i++){
+            if(visited[i]==0){
+                if(isCyclic(adj,visited,i)){
+                    return false;
+                }
+            }
+        }
+        return true;
+    }
+};

Solutions/Russian_Doll_Envelope.cpp

@@ -0,0 +1,23 @@
+#include<bits/stdc++.h>
+using namespace std;
+
+// Problem Statement : https://leetcode.com/problems/russian-doll-envelopes/
+
+//Similar to LIS with a tweak.
+int maxEnvelopes(vector<vector<int>>& envelopes) {
+    sort(envelopes.begin(),envelopes.end());
+    int n=envelopes.size(),res=1;
+    vector<int>dp(n,1);
+    for(int i=1;i<n;i++){
+        for(int j=0;j<i;j++){
+            if(envelopes[i][0]>envelopes[j][0] && envelopes[i][1]>envelopes[j][1]){
+                dp[i] = max(dp[i],1+dp[j]);
+            }
+        }
+        res = max(res,dp[i]);
+    }
+    if(n==0) return 0;
+    else return res;
+}
+
+