A next greater element LeetCode 503. II (Next Greater Element II)

503. The next element of a larger II
503. Greater the Next Element II

Title Description
Given a loop array (the last element of the next element is the first element of the array), the output of each element of the next higher element. The next element of a larger number x is based on an array traversal order, bigger than its first number after this number, which means that you should search for its next cycle of a larger number. If not, then the output of -1.

LeetCode503. Next Greater Element II中等

Example 1:

Input: [1,2,1]
Output: [2, 1,2]
Explanation: at first a larger number is 1 2; a larger number can not be found under the numbers 2; the second the next largest number of cycles required 1 search result is 2.

Note: the length of the input array does not exceed 10000.

Java implementation
brute force

import java.util.Arrays;

class Solution {
    public int[] nextGreaterElements(int[] nums) {
        int n = nums.length;
        int[] res = new int[n];
        Arrays.fill(res, -1);
        for (int i = 0; i < n; i++) {
            for (int j = i + 1; j < i + n; j++) {
                if (nums[j % n] > nums[i]) {
                    res[i] = nums[j % n];
                    break;
                }
            }
        }
        return res;
    }
}

Stack Stack

import java.util.Arrays;
import java.util.Stack;

class Solution {
    public int[] nextGreaterElements(int[] nums) {
        int n = nums.length;
        Stack<Integer> stack = new Stack<>();
        int[] res = new int[n];
        Arrays.fill(res, -1);
        for (int i = 0; i < 2 * n; i++) {
            int num = nums[i % n];
            while (!stack.isEmpty() && num > nums[stack.peek()]) {
                res[stack.pop()] = num;
            }
            if (i < n) {
                stack.push(i);
            }
        }
        return res;
    }
}

Similar topics

• 496. Under a greater element I Next Greater Element I
• A next greater element 556. III Next Greater Element III

Reference material

• https://leetcode.com/problems/next-greater-element-ii/
• https://leetcode-cn.com/problems/next-greater-element-ii/