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456. 132 Pattern Given a sequence of n integers a1, a2, ..., an, a 132 pattern is a subsequence ai, aj, ak such that i < j < k and ai < ak < aj. Design an algorithm that takes a list of n numbers as input and checks whether there is a 132 pattern in the list. Note: n will be less than 15,000. Example 1: Input: [1, 2, 3, 4] Output: False Explanation: There is no 132 pattern in the sequence. Example 2: Input: [3, 1, 4, 2] Output: True Explanation: There is a 132 pattern in the sequence: [1, 4, 2]. Example 3: Input: [-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]. //https://discuss.leetcode.com/topic/67881/single-pass-c-o-n-space-and-time-solution-8-lines-with-detailed-explanation public class Solution { public boolean find132pattern(int[] nums) { int s3 = Integer.MIN_VALUE; Stack st = new Stack(); for(int i = nums.length-1; i >= 0; i--){ if(nums[i] < s3) { return true; } while(!st.empty() && nums[i] > st.peek() ) { s3 = st.pop(); } st.push(nums[i]); } return false; } }