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.length
• 1 <= n <= 2 * 105
• -109 <= nums[i] <= 109

Solutions (Rust)

1. Solution

impl Solution {
    pub fn find132pattern(nums: Vec<i32>) -> bool {
        let mut stack = vec![];
        let mut min_num = i32::MAX;

        for k in 0..nums.len() {
            while let Some(&(numsi, numsj)) = stack.last() {
                if numsi < nums[k] && nums[k] < numsj {
                    return true;
                } else if nums[k] >= numsj {
                    stack.pop();
                } else {
                    break;
                }
            }

            stack.push((min_num, nums[k]));
            min_num = min_num.min(nums[k]);
        }

        false
    }
}