673. Number of Longest Increasing Subsequence

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Problem

Given an integer array nums, return the number of longest increasing subsequences.

Notice that the sequence has to be strictly increasing.

Example 1:

Input: nums = [1,3,5,4,7]
Output: 2
Explanation: The two longest increasing subsequences are [1, 3, 4, 7] and [1, 3, 5, 7].

Example 2:

Input: nums = [2,2,2,2,2]
Output: 5
Explanation: The length of the longest increasing subsequence is 1, and there are 5 increasing subsequences of length 1, so output 5.

Constraints:

• 1 <= nums.length <= 2000
• $-10^6 <= nums[i] <= 10^6$

Code

300. Longest Increasing Subsequence

class Solution {
    public int findNumberOfLIS(int[] nums) {
        int maxLen = 1;

        int[] dp = new int[nums.length];
        int[] count = new int[nums.length];
        dp[0] = 1;
        count[0] = 1;

        for(int i = 1; i < nums.length; i++) {
            dp[i] = 1;
            int maxCount = 1;
            for(int j = 0; j < i; j++) {
                if(nums[j] < nums[i]) {
                    if(dp[j] + 1 == dp[i]) {
                        maxCount += count[j];
                    } else if (dp[j] + 1 > dp[i]) {
                        maxCount = count[j];
                        dp[i] = dp[j] + 1;
                    }
                }
            }

            count[i] = maxCount;
            maxLen = Math.max(maxLen, dp[i]);
        }

        int res = 0;

        for(int i = 0; i < nums.length; i++) {
            if(dp[i] == maxLen) {
                res += count[i];
            }
        }

        return res;
    }
}