Featured image of post LeetCode 75 - 334. Increasing Triplet Subsequence

LeetCode 75 - 334. Increasing Triplet Subsequence

Description

Given an integer array nums, return true if there exists a triple of indices (i, j, k) such that i < j < k and nums[i] < nums[j] < nums[k]. If no such indices exists, return false.

Example 1:

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Input: nums = [1,2,3,4,5]
Output: true
Explanation: Any triplet where i < j < k is valid.

Example 2:

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Input: nums = [5,4,3,2,1]
Output: false
Explanation: No triplet exists.

Example 3:

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Input: nums = [2,1,5,0,4,6]
Output: true
Explanation: The triplet (3, 4, 5) is valid because nums[3] == 0 < nums[4] == 4 < nums[5] == 6.

Constraints:

  • 1 <= nums.length <= 5 * 10^5
  • -2^31 <= nums[i] <= 2^31 - 1

Solutions

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class Solution {
public:
    bool increasingTriplet(vector<int>& nums) {
        if (nums.size() < 3) {
            return false;
        }
        int first = nums[0];
        int second = std::numeric_limits<int>::max();
        
        for (int i = 1; i < nums.size(); i++) {
            // third is greater than second
            if (nums[i] > second) {
                return true;
            } 
            // third is less than second,but greate than first
            else if (nums[i] > first) {
                second = nums[i];
            }
            // third is less than first
            else {
                first = nums[i];
            }
        }
        return false;
    }
};
Licensed under CC BY-NC-SA 4.0
Last updated on Jan 08, 2024 21:43 +0800