Sum to N--DFS

分析：類似表達式的問題都用DFS

Code：

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
 
int n, ans;
 
void dfs(int sum, int k) {
    if(k == n-1) {
        if(sum == k+1) ans++;
        return;
    }
    dfs(sum+k+1, k+1);
    dfs(sum-k-1, k+1);
}
 
int main() {
    while(~scanf("%d", &n)) {
        ans = 0;
        dfs(-1+2, 2);
        dfs(-1-2, 2);
        printf("%d\n", ans);
    }
 
 
 
    return 0;
}