503 Next Greater Element II¶

Problem:¶

Given a circular array (the next element of the last element is the first element of the array), print the Next Greater Number for every element. The Next Greater Number of a number x is the first greater number to its traversing-order next in the array, which means you could search circularly to find its next greater number. If it doesn't exist, output -1 for this number.

Example 1:

Input: [1,2,1]
Output: [2,-1,2]
Explanation: The first 1's next greater number is 2; 
The number 2 can't find next greater number; 
The second 1's next greater number needs to search circularly, which is also 2.

Note: The length of given array won't exceed 10000.

Solutions:¶

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