673. Number of Longest Increasing Subsequence

Medium (Trung bình) C++ 🔗 Xem trên LeetCode

📋 Đề Bài

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
  • -106 <= nums[i] <= 106

💻 Lời Giải

C++ 0673-number-of-longest-increasing-subsequence.cpp 
class Solution {
public:
    int findNumberOfLIS(vector<int>& nums) {
        int n = nums.size();
        vector<int> lis(n, 1), cnt(n, 1);
        int maxLen = 1;
        for (int i = 1; i < n; ++i) {
            for (int j = 0; j < i; ++j) {
                if (nums[j] < nums[i] and lis[i] < lis[j] + 1) {
                    lis[i] = lis[j] + 1;
                    cnt[i] = cnt[j];
                }
                else if (lis[i] == lis[j] + 1) {
                    cnt[i] += cnt[j];
                }
            }
            maxLen = max(maxLen, lis[i]);
        }
        int ans = 0;
        for (int i = 0; i < n; ++i) {
            if (lis[i] == maxLen) {
                ans += cnt[i];
            }
        }
        return ans;
    }
};