DFS-生日蛋糕

生日蛋糕

一道深搜题，看了这两个博客才懂的。

http://blog.csdn.net/blesslzh0108/article/details/53486168

http://blog.csdn.net/v5zsq/article/details/46575215

 

#include<iostream>
#include<algorithm>
#include<cstdio>
using namespace std;
const int maxn = 0x3f3f3f3f;
int minv[21], mins[21];
int ans, mh,n, m;

void dfs(int v, int s, int level, int r, int h)
{
    if (level == 0) {
        if (v == n&&s < ans)
            ans = s;
        return;
    }
    if (v + minv[level - 1] > n) return;
    if (s + mins[level - 1] > ans) return;
    if (2 * (n - v) / r + s >= ans) return;
    for (int i = r - 1; i >= level; i--) {
        if (level == m) s = i*i;
        mh = min(h - 1, (n - v - minv[level - 1]) / (i*i));
        for (int j = mh; j >= level; j--)
            dfs(v + i*i*j, s + 2 * i*j, level - 1, i, j);
    }
}

int main()
{
    minv[0] = 0, mins[0] = 0;
    for (int i = 1; i <= 20; i++) {
        minv[i] = minv[i - 1] + i*i*i;
        mins[i] = mins[i - 1] + 2 * i*i;
    }
    while (scanf("%d%d",&n,&m)==2)
    {
        ans = maxn;
        dfs(0, 0, m, n + 1, n + 1);
        if (ans == maxn)  ans = 0;
        printf("%d\n", ans);
    }
    return 0;
}