300. Longest Increasing Subsequence

Alen Alex · February 17, 2026

LeetCode Link: 300. Longest Increasing Subsequence
Language: C#

Problem Statement

Given an integer array nums, return the length of the longest strictly increasing subsequence.

Example 1:

Input: nums = [10,9,2,5,3,7,101,18]
Output: 4
Explanation: The longest increasing subsequence is [2,3,7,101], therefore the length is 4.

Example 2:

Input: nums = [0,1,0,3,2,3]
Output: 4

Example 3:

Input: nums = [7,7,7,7,7,7,7]
Output: 1

Constraints:

  • 1 <= nums.length <= 2500
  • -104 <= nums[i] <= 104

Solution

public class Solution {
    public int LengthOfLIS(int[] nums) {
        var n = nums.Length;
        var dp = new int[n];
        var max = 1;
        Array.Fill(dp, 1);

        for (int i=n-1; i>=0; i--)
        {
            for (int j=i+1; j<n; j++)
            {
                if (nums[i] < nums[j])
                {
                    dp[i] = Math.Max(dp[i], 1 + dp[j]);
                    max = Math.Max(dp[i], max);
                }
            }
        }

        return max;
    }
}

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