9D - How many trees - CodeForces Solution


combinatorics divide and conquer dp *1900

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Python Code:


f = {}
dp = {}


def get_f(n):
    if n in f:
        return f[n]
    if n == 0:
        return 1
    res = 0
    for i in range(0, n):
        res += get_f(i) * get_f(n - 1 - i)
    f[n] = res
    return res


def get_dp(n, h):
    if (n, h) in dp:
        return dp[n, h]
    if h > n:
        return 0
    if n <= 1:
        return 1
    res = 0
    for i in range(0, n):
        res += get_dp(i, h - 1) * get_f(n - i - 1) + \
            get_dp(n - i - 1, h - 1) * get_f(i) - \
            get_dp(i, h - 1) * get_dp(n - i - 1, h - 1)
    dp[n, h] = res
    return res


n, h = map(int, input().split())
print(get_dp(n, h))

C++ Code:

#include <bits/stdc++.h>
using namespace std;

int main(){
    int n, k;
    cin >> n >> k;
    long long d[n+1][n+1];
    memset(d, 0, sizeof(d));
    d[0][0] = d[1][1] = 1;
    for(int i=2; i <= n; i++){
        for(int j=2; j <= n; j++){
            for(int o=0; o<i; o++){
                long long l=0, r=0;
                for(int h=0; h<j; h++){
                    l += d[o][h], r += d[i-o-1][h];
                }
                d[i][j] += l * d[i-o-1][j-1] - d[i-o-1][j-1] * d[o][j-1] + r * d[o][j-1];
            }
        }
    }
    long long wa=0;
    for(int i=k; i <= n; i++) wa += d[n][i];
    cout << wa;
    return 0;
}


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