• Question
• Solution

Question

Given an unsorted array of integers, find the length of longest increasing subsequence.

For example, Given [10, 9, 2, 5, 3, 7, 101, 18], The longest increasing subsequence is [2, 3, 7, 101], therefore the length is 4. Note that there may be more than one LIS combination, it is only necessary for you to return the length.

Your algorithm should run in $O(n^2)$ complexity.

Follow up: Could you improve it to O(n log n) time complexity?

Solution

Result: Accepted Time: 36 ms

Here should be some explanations.

int dp[65535];
int lengthOfLIS(int* nums, int nsz) {
    dp[0] = 1;
    int ret = nsz&1;
    for(int i = 1; i < nsz; i++)
    {
        int value = 0;
        for(int j = 0; j < i; j++)
            if(nums[j] < nums[i] && dp[j] > value)
                value = dp[j];
        dp[i] = value+1;
        if(dp[i] > ret)
            ret = dp[i];
    }
    return ret;
}

Complexity Analytics

• Time Complexity: $O(n^2)$
• Space Complexity: $O(1)$