LeetCode Increasing Triplet Subsequence

Description:

Given an unsorted array return whether an increasing subsequence of length 3 exists or not in the array.

Formally the function should:

Return true if there exists  i, j, k 
such that  arr[i] <  arr[j] <  arr[k] given 0 ≤  i <  j <  k ≤  n-1 else return false.

Your algorithm should run in O(n) time complexity and O(1) space complexity.

Solution:

模拟LIS的做法，不过只需要记录最小的两个就好。

因为是递增，所以在符合 

if (nums[i] > min_1 && nums[i] < min_2)

情况下，再给第二小的赋值

min_2 = nums[i];

Code:

public class Solution {
	public boolean increasingTriplet(int[] nums) {
		int len = nums.length;
		if (len <= 2)
			return false;
		int min_1 = Integer.MAX_VALUE;
		int min_2 = Integer.MAX_VALUE;

		for (int i = 0; i < len; i++) {
			if (nums[i] > min_2) {
				return true;
			}
			if (nums[i] < min_1) {
				min_1 = nums[i];
			} else if (nums[i] > min_1 && nums[i] < min_2) {
				min_2 = nums[i];
			}
		}

		return false;
	}
}