Create Day 15 Maximum Sum Circular Subarray.cpp

Author: tusharjaiswal123

Day 15 Maximum Sum Circular Subarray.cpp

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+PROBLEM:
+
+
+Given a circular array C of integers represented by A, find the maximum possible sum of a non-empty subarray of C.
+Here, a circular array means the end of the array connects to the beginning of the array.  (Formally, C[i] = A[i] when
+0 <= i < A.length, and C[i+A.length] = C[i] when i >= 0.)
+Also, a subarray may only include each element of the fixed buffer A at most once.  (Formally, for a subarray C[i],
+C[i+1], ..., C[j], there does not exist i <= k1, k2 <= j with k1 % A.length = k2 % A.length.)
+
+ 
+Example 1:
+Input: [1,-2,3,-2]
+Output: 3
+Explanation: Subarray [3] has maximum sum 3
+
+Example 2:
+Input: [5,-3,5]
+Output: 10
+Explanation: Subarray [5,5] has maximum sum 5 + 5 = 10
+
+Example 3:
+Input: [3,-1,2,-1]
+Output: 4
+Explanation: Subarray [2,-1,3] has maximum sum 2 + (-1) + 3 = 4
+
+Example 4:
+Input: [3,-2,2,-3]
+Output: 3
+Explanation: Subarray [3] and [3,-2,2] both have maximum sum 3
+
+Example 5:
+Input: [-2,-3,-1]
+Output: -1
+Explanation: Subarray [-1] has maximum sum -1
+ 
+Note:
+
+1. -30000 <= A[i] <= 30000
+2. 1 <= A.length <= 30000
+
+
+
+SOLUTION:
+
+
+class Solution {
+    private:
+    
+    int kadane(vector<int>& A)
+    {
+        int ans=INT_MIN,s=0;
+        
+        for(auto k:A)
+        {
+            s=max(s+k,k);
+            ans=max(ans,s);
+        }
+        
+        return ans;
+    }
+    
+public:
+    int maxSubarraySumCircular(vector<int>& A) {
+        
+        int s1,s2,i,n,s=0,ans;
+        s1=kadane(A);       // if max subarray is in middle
+        
+        n=A.size();
+        
+        for(i=0;i<n;i++)
+        {
+            s+=A[i];
+            A[i]=-A[i];
+        }
+        
+        s2=kadane(A);      //max subarray sum with negative elements
+        
+        if(s+s2==0)
+            ans=s1;
+        else
+            ans=max(s1,s+s2);
+        
+        return ans;
+        
+    }
+};