[LeetCode] (medium) 673. Number of Longest Increasing Subsequence

https://leetcode.com/problems/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.

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二分搜索插入點，再二分搜索累加值，注意邊界情況。 

class Solution {
public:
    int findNumberOfLIS(vector<int>& nums) {
        if(nums.empty()) return 0;
        vector<vector<pair<int, int>>> arr;
        int idx;
        int pre_num, pre_idx;
        for(int cur : nums){
            // cout << cur << ' ';
            idx = binary_search(arr, cur);
            // cout << idx << ' ';
            if(idx == arr.size()) arr.push_back(vector<pair<int, int>>());
            if(idx == 0){
                // if(arr[idx].size() != 0) arr[idx].push_back(pair<int, int>(cur, arr[idx].back().second+1));
                // else arr[idx].push_back(pair<int, int>(cur, 1));
                if(arr[idx].size() != 0) arr[idx].emplace_back(cur, arr[idx].back().second+1);
                else arr[idx].emplace_back(cur, 1);
            }else{
                pre_idx = binary_search_sec(arr[idx-1], cur);
                // cout << pre_idx << ' ';
                if(pre_idx == -1){
                    pre_num = arr[idx-1].back().second;
                }else{
                    pre_num = arr[idx-1].back().second - arr[idx-1][pre_idx].second;
                }
                // if(arr[idx].size() != 0) arr[idx].push_back(pair<int, int>(cur, pre_num+arr[idx].back().second));
                // else arr[idx].push_back(pair<int, int>(cur, pre_num));
                if(arr[idx].size() != 0) arr[idx].emplace_back(cur, pre_num+arr[idx].back().second);
                else arr[idx].emplace_back(cur, pre_num);
            }
            // cout << endl;
        }
        
        return arr.back().back().second;
    }
    
    int binary_search(vector<vector<pair<int, int>>> &arr, int target){
        int lo = -1, hi = arr.size()-1;
        int mid;
        while(lo < hi){
            mid = (lo+hi+1)/2;
            if(target > arr[mid].back().first) lo = mid;
            else hi = mid-1;
        }
        return hi+1;
    }
    
    int binary_search_sec(vector<pair<int, int>> &arr, int target){
        int lo = 0, hi = arr.size();
        int mid;
        while(lo < hi){
            mid = (lo+hi)/2;
            if(target > arr[mid].first) hi = mid;
            else lo = mid+1;
        }
        return hi-1;
    }
};