334. Increasing Triplet Subsequence

Posted 2020-08-12 Machelsky

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.

Examples:
Given [1, 2, 3, 4, 5],
return true.

Given [5, 4, 3, 2, 1],
return false.

Credits:

思路：碰到比小的就更新。参考discussion

public class Solution {
    public boolean increasingTriplet(int[] nums) {
        int small=Integer.MAX_VALUE;
        int big=Integer.MAX_VALUE;
        for(int m:nums){
            if(m<=small){
                small=m;
            }else if(m<=big){
                big=m;
            }else{
                return true;
            }
        }
        return false;
    }
}