152.maximum-product-subarray.js

/*
 * @lc app=leetcode id=152 lang=javascript
 *
 * [152] Maximum Product Subarray
 *
 * https://leetcode.com/problems/maximum-product-subarray/description/
 *
 * algorithms
 * Medium (28.61%)
 * Total Accepted:    202.8K
 * Total Submissions: 700K
 * Testcase Example:  '[2,3,-2,4]'
 *
 * Given an integer array nums, find the contiguous subarray within an array
 * (containing at least one number) which has the largest product.
 *
 * Example 1:
 *
 *
 * Input: [2,3,-2,4]
 * Output: 6
 * Explanation: [2,3] has the largest product 6.
 *
 *
 * Example 2:
 *
 *
 * Input: [-2,0,-1]
 * Output: 0
 * Explanation: The result cannot be 2, because [-2,-1] is not a subarray.
 *
 */
/**
 * @param {number[]} nums
 * @return {number}
 */
var maxProduct = function(nums) {
  // let max = nums[0];
  // let temp = null;
  // for(let i = 0; i < nums.length; i++) {
  //     temp = nums[i];
  //     max = Math.max(temp, max);
  //     for(let j = i + 1; j < nums.length; j++) {
  //         temp *= nums[j];
  //         max = Math.max(temp, max);
  //     }
  // }

  // return max;
  let max = nums[0];
  let min = nums[0];
  let res = nums[0];

  for (let i = 1; i < nums.length; i++) {
    let tmp = min;
    min = Math.min(nums[i], Math.min(max * nums[i], min * nums[i])); // 取最小
    max = Math.max(nums[i], Math.max(max * nums[i], tmp * nums[i])); /// 取最大
    res = Math.max(res, max);
  }
  return res;
};