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[Java教程]334. Increasing Triplet Subsequence


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.

代码如下:

 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 }