Given an array of n integers nums, a 132 pattern is a subsequence of three integers nums[i], nums[j] and nums[k] such that i < j < k and nums[i] < nums[k] < nums[j].
Return true if there is a 132 pattern in nums, otherwise, return false.
Example 1:
Input: nums = [1,2,3,4]
Output: false
Explanation: There is no 132 pattern in the sequence.
Example 2:
Input: nums = [3,1,4,2]
Output: true
Explanation: There is a 132 pattern in the sequence: [1, 4, 2].
Example 3:
Input: nums = [-1,3,2,0]
Output: true
Explanation: There are three 132 patterns in the sequence: [-1, 3, 2], [-1, 3, 0] and [-1, 2, 0].
Constraints:
-
n == nums.length -
1 <= n <= 2 * 105 -
-109 <= nums[i] <= 109
SOLUTION:
class Solution:
def find132pattern(self, nums: List[int]) -> bool:
n = len(nums)
if n < 3:
return False
stack = []
k = -1
for i in range(n - 1, -1, -1):
if k > -1 and nums[k] > nums[i]:
return True
while len(stack) > 0 and nums[i] > nums[stack[-1]]:
k = stack.pop()
stack.append(i)
return False
# class Solution:
# def makeSeg(self, arr, i, j):
# seg = self.seg
# if (i, j) in seg:
# return seg[(i, j)]
# if i == j:
# seg[(i, j)] = arr[i]
# return arr[i]
# mid = (i + j) // 2
# curr = max(self.makeSeg(arr, i, mid), self.makeSeg(arr, mid + 1, j))
# seg[(i, j)] = curr
# return curr
# def getMax(self, arr, i, j, ni, nj):
# seg = self.seg
# if ni >= i and nj <= j:
# return seg[(ni, nj)]
# if (ni < i and nj < i) or (ni > j and nj > j):
# return float('-inf')
# mid = (ni + nj) // 2
# return max(self.getMax(arr, i, j, ni, mid), self.getMax(arr, i, j, mid + 1, nj))
# def find132pattern(self, nums: List[int]) -> bool:
# n = len(nums)
# self.seg = {}
# self.makeSeg(nums, 0, n - 1)
# for i in range(n):
# for j in range(i + 2, n):
# if nums[j] > nums[i] and self.getMax(nums, i, j, 0, n - 1) > nums[j]:
# return True
# return False
# class Solution:
# def find132pattern(self, nums: List[int]) -> bool:
# n = len(nums)
# next_lowest = [n for i in range(n)]
# stack = []
# for i in range(n):
# while len(stack) > 0 and nums[i] < nums[stack[-1]]:
# curr = stack.pop()
# next_lowest[curr] = i
# for j in range(curr):
# if nums[j] < nums[i]:
# return True
# stack.append(i)
# return False
# class Solution:
# def find132pattern(self, nums: List[int]) -> bool:
# currMin = float('inf')
# currMax = float('-inf')
# for num in nums:
# currMin = min(currMin, num)
# currMax = max(currMax, num)
# if num > currMin and num < currMax:
# return True
# return False
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