leetcode 503

next_greater_element_II.kt

class Solution {
    fun nextGreaterElements(nums: IntArray): IntArray {
        val longerNums = IntArray(nums.size*2)
        for(i in nums.indices) {
            longerNums[i] = nums[i]
            longerNums[nums.size+i] = nums[i]
        }
        
        val nextGreatNumber = IntArray(longerNums.size)
        val stack = mutableListOf<Int>()
        
        for(i in longerNums.lastIndex downTo 0) {
            while(stack.isNotEmpty() && longerNums[i] >= stack.last()) {
                stack.removeAt(stack.lastIndex)
            }
            
            nextGreatNumber[i] = if(stack.isEmpty()) -1 else stack.last()
            stack.add(longerNums[i])
        }

        return nextGreatNumber.take(nums.size).toIntArray()
    }
}