Leetcode[152] Maximum Product Subarray

Leetcode[152] Maximum Product Subarray

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

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

DP

复杂度
O(N),O(1)

思路
要保留一个到某一位来看的最大值和最小值。因为在数组中有负数的出现，所以到这一位为止的能得到的最大值，可能是由之前的最大值和这个数相乘得到，也可能是最小值和这个数相乘得到的。

代码

public int maxProduct(int[] nums) {
    if(nums == null || nums.length == 0) return 0;
    int max = nums[0];
    int maxProduct = nums[0];
    int minProduct = nums[0];
    for(int i = 1; i < nums.length; i ++) {
        int prevMax = maxProduct;
        int prevMin = minProduct;
        maxProduct = Math.max(nums[i], Math.max(prevMax * nums[i], prevMin * nums[i]));
        minProduct = Math.min(nums[i], Math.min(prevMin * nums[i], prevMax * nums[i]));
        max = Math.max(max, maxProduct);
    }
    return max;
}