LeetCode334. Increasing Triplet Subsequence完美解答

/**

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.

*/

#include <iostream>

#include <vector>

using namespace std;

class Solution {

public:
bool increasingTriplet(vector<int>& nums) {
if (nums.size() < 3) {
return false;
}
int count = 1;
int min = nums[0];
int min2 = INT_MAX;
for (int i = 1; i < nums.size(); i++) {
if (nums[i] > min2) {
return true;
}
else if (nums[i] < min) {
min = nums[i];
}
else if (nums[i] < min2 && nums[i] > min) {
min2 = nums[i];
}
}
return false;
}

};