added max subarray sum (#131)

arrays/README.md

@@ -6,6 +6,7 @@
 2. [Dutch Flag Algo](c-or-cpp/dutch-flag-algo.cpp)
 3. [Left Rotation of Array](c-or-cpp/left-rotation.cpp)
 4. [Shift Negatives in Array](c-or-cpp/shift-negatives.cpp)
+5. [Maximum Subarray Sum](c-or-cpp/max-subarray-sum.cpp)
 
 ### Python
 
@@ -18,4 +19,3 @@
 ### Java
 
 1. [Counting Inversions](java/count-inversions.java)
-

arrays/c-or-cpp/max-subarray-sum.cpp

@@ -0,0 +1,69 @@
+#include<iostream>
+#include<climits>
+#define endl "\n"
+using namespace std;
+
+// Maximum Subarray Sum 
+
+// Approach A - Brute Force O(n^3)
+int maxSubArrSum_A(int a[],int n){
+    int maxSum = INT_MIN;
+    for(int i=0;i<n;++i){
+        for(int j=i;j<n;++j){
+            int sum = 0;
+            for(int k=i;k<=j;++k){
+                sum = sum + a[k];
+            }
+            maxSum = max(maxSum,sum);
+        }
+    }
+    return maxSum;
+}
+
+// Appraoch B - Cumulative Sum Approach O(n^2)
+int maxSubArrSum_B(int a[],int n){
+    int currSum[n+1]; currSum[0] = 0;
+    for(int i=1;i<=n;++i){
+        currSum[i] = currSum[i-1] + a[i-1];
+    }
+    int maxSum = INT_MIN;
+    for(int i=1;i<=n;++i){
+        for(int j=0;j<i;++j){
+            int sum = 0;
+            sum =  currSum[i] - currSum[j];
+            maxSum = max(maxSum,sum);
+        }
+    }
+    return maxSum;
+}
+
+// Approach C - Kadane's Algo O(n)
+int maxSubArrSum_C(int a[],int n){
+    int currSum=0;
+    int maxSum = INT_MIN;
+    for(int i=0;i<n;++i){
+        currSum += a[i];
+        if(currSum < 0) currSum = 0;
+        maxSum = max(maxSum,currSum);
+    }
+    
+    return maxSum;
+}
+
+//Utility function to print array
+void printArr(int a[],int n){
+    for(int i=0;i<n;++i) cout<<a[i]<<" ";
+    cout<<endl;
+}
+
+
+int main(){
+    //Some sample test cases
+    int a[] = {5,6,0,4,-1,4,7,2}; // n=8
+    int b[] = {4,-4,6,-6,10,-11,12}; // n=7
+    int c[] = {3,4,1,0,-2,-6,8,3}; // n=8
+    cout<<maxSubArrSum_A(b,7)<<endl;
+    cout<<maxSubArrSum_B(b,7)<<endl;
+    cout<<maxSubArrSum_C(b,7)<<endl;
+    return 0;
+}