456. 132 Pattern - Explanation

class Solution:
    def find132pattern(self, nums: List[int]) -> bool:
        n = len(nums)

        for k in range(2, n):
            for j in range(k - 1, 0, -1):
                if nums[j] <= nums[k]:
                    continue

                for i in range(j - 1, -1, -1):
                    if nums[i] < nums[k]:
                        return True

        return False

class Solution:
    def find132pattern(self, nums: List[int]) -> bool:
        stack = []  # pair [num, minLeft], mono decreasing
        curMin = nums[0]

        for i in range(1, len(nums)):
            while stack and nums[i] >= stack[-1][0]:
                stack.pop()
            if stack and nums[i] > stack[-1][1]:
                return True

            stack.append([nums[i], curMin])
            curMin = min(curMin, nums[i])

        return False

class Solution:
    def find132pattern(self, nums: List[int]) -> bool:
        stack, k = [], float('-inf')

        for i in range(len(nums) - 1, -1, -1):
            if nums[i] < k:
                return True

            while stack and stack[-1] < nums[i]:
                k = stack.pop()
            stack.append(nums[i])

        return False

class Solution:
    def find132pattern(self, nums: List[int]) -> bool:
        n = len(nums)
        stkTop, k = n, float('-inf')

        for i in range(n - 1, -1, -1):
            if nums[i] < k:
                return True

            while stkTop < n and nums[i] > nums[stkTop]:
                k = nums[stkTop]
                stkTop += 1

            stkTop -= 1
            nums[stkTop] = nums[i]

        return False