Let's assume the array contains both negative and positive values. We will keep track of the beginning and end of the current sub-array which gives us the greatest sum. // Find. max contiguous subarray void subArray(const vector& arr, int& start, int& end, int& sum) { if (arr.empty()) return; sum = 0; int currSum(0), i(0), j(0); for ( ; i = 0) currSum += arr[j++]; else { // found a new subarray with greater sum ==> update variables if (currSum > sum) { sum = currSum; start = i; end = j-1; } // reset variables currSum = 0; i = ++j; } } // edge case - very large number in the last position if (currSum > sum) { sum = currSum; start = i; end = j-1; } }