生日蛋糕

书上剪枝得很详细了，但是没有附上代码

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

int N, M;
int minV[21] = { 0 }, minA[21] = {0};
int min_area=1<<30;
int area = 0;


void Read()
{
	scanf("%d%d", &N, &M);
	for (int i = 1; i <= M; i++)
	{
		minV[i] = minV[i - 1] + i * i*i;
		minA[i] = minA[i - 1] + 2 * i*i;
	}
}

void DF(int v,int s,int dep,int maxR,int maxH)
//从下往上深搜，当前搭第dep层，当前已经搭的体积v，已有表面积s,还剩的层数dep，
//当前层（从上往下dep层）的最大半径maxR和高maxH(下一层的半径和高)
{
	if (v > N)
		return;
	if (dep == 0)
	{
		if(v==N)
		{
			if (s < min_area)
			{
				min_area = s;
			}
		}
		return;
	}
	if (v + minV[dep] > N || s + minA[dep] >= min_area || s + (N - v) * 2 / (maxR-1) >= min_area)
		return;
	for (int r = maxR-1 ; r >=dep ; r--)
	{   
		if (dep == M)
			s = r * r;
		for (int h =  min(maxH-1,(N-v-minV[dep-1])/(r*r)) ; h >=dep ; h--)
		{
				DF(v + r * r * h, s + 2 * r * h,dep - 1, r , h );
		}
	}
}

int main()
{
	Read();
	DF(0,0, M, sqrt(N)+1, N+1);
	if (min_area == 1 << 30)
		printf("0");
	else
		printf("%d",min_area);
	return 0;
}