index.js

/*
 * @lc app=leetcode id=496 lang=javascript
 *
 * [496] Next Greater Element I
 *
 * https://leetcode.com/problems/next-greater-element-i/description/
 *
 * algorithms
 * Easy (58.43%)
 * Total Accepted:    90.2K
 * Total Submissions: 152.7K
 * Testcase Example:  '[4,1,2]\n[1,3,4,2]'
 *
 * 
 * You are given two arrays (without duplicates) nums1 and nums2 where nums1’s
 * elements are subset of nums2. Find all the next greater numbers for nums1's
 * elements in the corresponding places of nums2. 
 * 
 * 
 * 
 * The Next Greater Number of a number x in nums1 is the first greater number
 * to its right in nums2. If it does not exist, output -1 for this number.
 * 
 * 
 * Example 1:
 * 
 * Input: nums1 = [4,1,2], nums2 = [1,3,4,2].
 * Output: [-1,3,-1]
 * Explanation:
 * ⁠   For number 4 in the first array, you cannot find the next greater number
 * for it in the second array, so output -1.
 * ⁠   For number 1 in the first array, the next greater number for it in the
 * second array is 3.
 * ⁠   For number 2 in the first array, there is no next greater number for it
 * in the second array, so output -1.
 * 
 * 
 * 
 * Example 2:
 * 
 * Input: nums1 = [2,4], nums2 = [1,2,3,4].
 * Output: [3,-1]
 * Explanation:
 * ⁠   For number 2 in the first array, the next greater number for it in the
 * second array is 3.
 * ⁠   For number 4 in the first array, there is no next greater number for it
 * in the second array, so output -1.
 * 
 * 
 * 
 * 
 * Note:
 * 
 * All elements in nums1 and nums2 are unique.
 * The length of both nums1 and nums2 would not exceed 1000.
 * 
 * 
 */
/**
 * @param {number[]} nums1
 * @param {number[]} nums2
 * @return {number[]}
 */
var nextGreaterElement = function(nums1, nums2) {
    const stack = [];
    const map = nums2.reduce((res, cur, index) => {
        while (stack.length > 0 && cur > stack[stack.length - 1]) {
            res[stack.pop()] = cur;
        }
        stack.push(cur);
        return res;
    }, {});
    return nums1.map((num) => {
        if (map[num]) {
            return map[num];
        }
        return -1;
    });
};

console.log(nextGreaterElement([4,1,2], [1,3,4,2]))

module.exports = {
    id:'496',
    title:'Next Greater Element I',
    url:'https://leetcode.com/problems/next-greater-element-i/description/',
    difficulty:'Easy',
}