POJ1190生日蛋糕[DFS 剪枝]

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <cmath>
using namespace std;
const int N=20;
int n,m,ans=1e9;
int mnv[N],mns[N];
void init(){
    for(int i=1;i<=m;i++){
        mnv[i]=mnv[i-1]+i*i*i;
        mns[i]=mns[i-1]+2*i*i;
    }
}
void dfs(int d,int lh,int lr,int s,int v){
    if(d==0){
        if(v==n&&s<ans) ans=s;
        return;
    }
    if(v+mnv[d]>n||s+mns[d]>ans) return;
    if(2*(n-v)/lr+s>ans) return;
    for(int tr=lr-1;tr>=d;tr--){
        if(d==m) s=tr*tr;
        int mxh=min(lh-1,(n-mnv[d-1]-v)/(tr*tr));
        for(int th=mxh;th>=d;th--){
            dfs(d-1,th,tr,s+2*th*tr,v+tr*tr*th);
        }
    }
}
int main(){
    scanf("%d%d",&n,&m);
    init();
    dfs(m,n-mnv[m-1],sqrt(n-mnv[m-1])+1,0,0);
    printf("%d",ans);
}