LeetCode 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

.
参考：大海里的太阳

维护两个数的递增序列，如果能找到第三个数比前两个大，则返回true。

设置一个small，一个big，small<big。如果能找到一个大于small和big的就返回true。时间复杂度为O(n)。

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