496.next-greater-element-i.java

/*
 * @lc app=leetcode id=496 lang=java
 *
 * [496] Next Greater Element I
 *
 * https://leetcode.com/problems/next-greater-element-i/description/
 *
 * algorithms
 * Easy (59.34%)
 * Likes:    844
 * Dislikes: 1369
 * Total Accepted:    102K
 * Total Submissions: 169.9K
 * 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.
 *
 *
 */
class Solution {
  public int[] nextGreaterElement(int[] nums1, int[] nums2) {
    int[] result = new int[nums1.length];

    HashMap<Integer, Integer> map = new HashMap<>();
    for (int i = 0; i < nums2.length; i++) {
      map.put(nums2[i], i);
    }

    for (int i = 0; i < nums1.length; i++) {
      boolean flag = false;
      for (int j = map.get(nums1[i]) + 1; j < nums2.length; j++) {
        if (nums2[j] > nums1[i]) {
          result[i] = nums2[j];
          flag = true;
          break;
        }
      }
      if (!flag) {
        result[i] = -1;
      }
    }

    return result;
  }
}