Given an integer array nums, find the contiguous subarray (containing at least one number) which has the largest sum and return its sum.
Example:
Input: [-2,1,-3,4,-1,2,1,-5,4],
Output: 6
Explanation: [4,-1,2,1] has the largest sum = 6.
Follow up:
If you have figured out the O(n) solution, try coding another solution using the divide and conquer approach, which is more subtle.
Solutions
My solution
class Solution {
public:
int maxSubArray(vector<int>& nums) {
int max_sum = INT_MIN; // maximum subarray sum
int sum = 0;
int min_sum = 0; // minimum sum of first k elements
for(int i = 0; i < nums.size(); ++i){
sum += nums[i];
max_sum = max(max_sum, sum - min_sum);
min_sum = min(min_sum, sum);
}
return max_sum;
}
};
A slightly more efficient solution
class Solution {
public:
int maxSubArray(vector<int>& nums) {
int ans = INT_MIN;
int max_sum = 0; // maximum sum of subarray ending with the previous element;
for(int i = 0; i < nums.size(); ++i){
// need to consider too cases to update max_sum
// case 1: without the previous element, i.e., use only the current element:
// max_sum = nums[i]
// case 2: with the previous element:
// max_sum = nums[i] + max_sum
max_sum = max(nums[i], nums[i] + max_sum);
ans = max(ans, max_sum);
}
return ans;
}
};
