题目链接

题目描述

思路

• 暴力循环（不解释了）
• 单调栈，哈希表
  • https://leetcode-cn.com/problems/next-greater-element-i/solution/xia-yi-ge-geng-da-yuan-su-i-by-leetcode-bfcoj/

测试用例建议为：2, 5, 3, 8, 7, 6, 9

public int[] nextGreaterElement(int[] nums1, int[] nums2) {
    Map<Integer, Integer> map = new HashMap<>(16);
    Deque<Integer> stack = new ArrayDeque<>();
    for (int i = nums2.length - 1; i >= 0; --i) {
        int num = nums2[i];
        while (!stack.isEmpty() && num >= stack.peek()) {
            stack.pop();
        }
        map.put(num, stack.isEmpty() ? -1 : stack.peek());
        stack.push(num);
    }
    int[] res = new int[nums1.length];
    for (int i = 0; i < nums1.length; ++i) {
        res[i] = map.get(nums1[i]);
    }
    return res;
}