Algorithm
Problem Name: 456. 132 Pattern
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.length1 <= n <= 2 * 105-109 <= nums[i] <= 109
Code Examples
#1 Code Example with Java Programming
Code -
Java Programming
class Solution {
public boolean find132pattern(int[] nums) {
if (nums.length < 3) {
return false;
}
int[] minTillIndex = new int[nums.length];
minTillIndex[0] = nums[0];
for (int idx = 1; idx < nums.length; idx++) {
minTillIndex[idx] = Math.min(minTillIndex[idx - 1], nums[idx]);
}
Stack < Integer> stack = new Stack<>();
for (int idx = nums.length - 1; idx >= 0; idx--) {
if (nums[idx] > minTillIndex[idx]) {
while (!stack.isEmpty() && stack.peek() < = minTillIndex[idx]) {
stack.pop();
}
if (!stack.isEmpty() && stack.peek() < nums[idx]) {
return true;
}
stack.push(nums[idx]);
}
}
return false;
}
}
Input
nums = [1,2,3,4]
Output
false
#2 Code Example with Javascript Programming
Code -
Javascript Programming
const find132pattern = function(nums) {
let [stack, s3] = [[], -Infinity]
for (let i = nums.length - 1; i >= 0; i--) {
if (nums[i] < s3) {
return true
}
while (stack[stack.length - 1] < nums[i]) {
s3 = stack.pop()
}
stack.push(nums[i])
}
return false
}
Input
nums = [1,2,3,4]
Output
false
#3 Code Example with Python Programming
Code -
Python Programming
class Solution:
def find132pattern(self, nums):
stack, s3 = [], -float("inf")
for n in nums[::-1]:
if n < s3: return True
while stack and stack[-1] < n: s3 = stack.pop()
stack.append(n)
return False
Input
nums = [3,1,4,2]
Output
true