LC 1569. Number of Ways to Reorder Array to Get Same BST

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class Solution {
public:
    #define LL long long
    const int mod=1E9+7;
    vector<vector<LL>> table;
    int numOfWays(vector<int>& nums) {
        int n=nums.size();
        table.resize(n+1);
        for(int i=0;i<=n;i++){
            table[i]=vector<LL> (i+1,1);
            for(int j=1;j<i;j++){
                table[i][j]=(table[i-1][j]+table[i-1][j-1])%mod;
            }
        }
        return dfs(nums)-1;
    }
    
    LL dfs(vector<int>& nums){
        int n=nums.size();
        if(n<=2) return 1;
        
        vector<int> leftarr, rightarr;
        
        for(int i=1;i<n;i++){
            if(nums[i]>nums[0]) rightarr.push_back(nums[i]);
            else leftarr.push_back(nums[i]);
        }
        
        LL leftres=dfs(leftarr);
        LL rightres=dfs(rightarr);
        
        return (table[n-1][leftarr.size()]*leftres%mod) * rightres %mod;
    }
};