Leetcode 673. Number of Longest Increasing Subsequence

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

Example 1:

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

Example 2:

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

Note: Length of the given array will be not exceed 2000 and the answer is guaranteed to be fit in 32-bit signed int.

Code (Java):

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class Solution {     public int findNumberOfLIS(int[] nums) {         if (nums == null || nums.length == 0) {             return 0;         }                   int[] lenDP = new int[nums.length];         int[] countDP = new int[nums.length];         int maxLen = 1;                   for (int i = 0; i < nums.length; i++) {             lenDP[i] = 1;             countDP[i] = 1;             for (int j = 0; j < i; j++) {                 if (nums[i] > nums[j]) {                     if (lenDP[i] < lenDP[j] + 1) {                         lenDP[i] = lenDP[j] + 1;                         countDP[i] = countDP[j];                         maxLen = Math.max(maxLen, lenDP[i]);                     } else if (lenDP[i] == lenDP[j] + 1) {                         countDP[i] += countDP[j];                     }                 }             }         }                   int count = 0;         for (int i = 0; i < lenDP.length; i++) {             if (lenDP[i] == maxLen) {                 count += countDP[i];             }         }                   return count;     } }