描述

You are given two integer arrays nums1 and nums2 both of unique elements, where nums1 is a 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, return -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:

1 <= nums1.length <= nums2.length <= 1000
0 <= nums1[i], nums2[i] <= 10^4
All integers in nums1 and nums2 are unique.
All the integers of nums1 also appear in nums2.

解析

根据题意，num1 是 num2 的子集，找出 num1 中每个元素在 num2 中的对应位置之后的第一个大于它的数，如果没有则结果为 -1 。我这里定义了一个方法 find ，就是为了在 num2 中的 idx 位置之后找比 nums2[idx] 大的数字。直接遍历 num1 ，得到元素在 num2 中的索引，然后使用我定义的 find 函数，得到的结果追加到 result 中，遍历结束即可得到结果。

解答

class Solution(object):
    def nextGreaterElement(self, nums1, nums2):
        """
        :type nums1: List[int]
        :type nums2: List[int]
        :rtype: List[int]
        """
        def find(A, idx):
            result = -1
            for i in range(idx, len(A)):
                if A[i]>A[idx]:
                    result = A[i]
                    break
            return result
        result = []
        for n in nums1:
            idx = nums2.index(n)
            result.append(find(nums2, idx))
        return result

运行结果

Runtime: 80 ms, faster than 21.98% of Python online submissions for Next Greater Element I.
Memory Usage: 13.3 MB, less than 100.00% of Python online submissions for Next Greater Element I.

原题链接：https://leetcode.com/problems/next-greater-element-i

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