Maximum Product Subarray / Maximum Subarray

Maximum Subarray

Example
Given the array [−2,2,−3,4,−1,2,1,−5,3], the contiguous subarray [4,−1,2,1] has the largest sum = 6.

public class Solution {
    /*
     * @param nums: A list of integers
     * @return: A integer indicate the sum of max subarray
     */
    public int maxSubArray(int[] nums) {
        // write your code here
        if (nums == null || nums.length == 0) {
            return Integer.MIN_VALUE;
        }
        
        int curSum = nums[0];
        int maxSum = nums[0];
        
        for (int i = 1; i < nums.length; i++) {
            curSum = curSum > 0 ? curSum + nums[i] : nums[i];
            maxSum = curSum > maxSum ? curSum : maxSum;
        }
        
        return maxSum;
    }
}

Maximum Product Subarray

Find the contiguous subarray within an array (containing at least one number) which has the largest product.

Example
For example, given the array [2,3,-2,4], the contiguous subarray [2,3] has the largest product = 6.

public int maxProduct(int[] nums) {
        // write your code here
        if (nums == null || nums.length == 0) {
            return 0;
        }
        int minPre = nums[0], maxPre = nums[0];
        int max = nums[0], min = nums[0];
        int res = nums[0];
        for (int i = 1; i < nums.length; i ++) {
            max = Math.max(nums[i], Math.max(maxPre * nums[i], minPre * nums[i]));
            min = Math.min(nums[i], Math.min(maxPre * nums[i], minPre * nums[i]));
            res = Math.max(res, max);
            maxPre = max;
            minPre = min;
        }
        return res;
    }