题解 | #有多少个不同的二叉搜索树#

#include <stdio.h>

int main() {
    
    // n -- int
    // arr -- int arr[100]

    int n = 0;
    int arr[20]= {0};

    scanf("%d", &n);
    
    arr[0] = 1;
    arr[1] = 1;
    arr[2] = 2;

    /*
    arr[3] = 1;
    v l r   lv           rv
    1 0 2   arr[0] 1     arr[2] 2 
    2 1 1   arr[1] 1     arr[1] 1
    3 2 0   arr[2] 2     arr[0] 1
    */
    for(int i = 3; i <= n; i ++ ){
       int sum = 0;
       for(int j = 1; j <= i; j ++){
          sum += (arr[j-1] * arr[i-j]);
       }
       arr[i] = sum;
    }
    printf("%d", arr[n]);
    
    return 0;
}