334. Increasing Triplet Subsequence，tripletsubsequence

334. Increasing Triplet Subsequence，tripletsubsequence

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.

代碼如下：

 1 public class Solution { 2     public boolean increasingTriplet(int[] nums) { 3          4         if(nums.length<3) 5         return false; 6          7         for(int i=nums.length-1;i>=2;i--) 8         { 9             int j=i-1;10             for( ;j>=1;j--)11             {12                 if(nums[i]>nums[j])13                 {14                        int k=j-1;15                        for(;k>=0;k--)16                        {17                            if(nums[j]>nums[k])18                            return true;19                        }20                 }21                22             }23 24         }25         return false;26     } 27 }