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# 334.Increasing-Triplet-Subsequence

## 334. Increasing Triplet Subsequence

## 题目地址

<https://leetcode.com/problems/increasing-triplet-subsequence/>

## 题目描述

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

Example 1:
Input: [1,2,3,4,5]
Output: true

Example 2:
Input: [5,4,3,2,1]
Output: false
```

## 代码

### Approach #1

Time: O(N) && Space: O(1)

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