POJ-1190 生日蛋糕 NOI99

#include <cstdio>
#include <iostream>
#include <fstream>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <queue>

#define rep(i, l, r) for(int i=l; i<=r; i++)
#define down(i, l, r) for(int i=l; i>=r; i--)
#define maxn 23
#define MAX 1<<30

using namespace std;

int n, m, ans, minv[maxn], mins[maxn];

void Search(int v, int s, int l, int R, int H)
{
    if (!l)
    {
        if (v == n && s < ans) 
            ans = s; 
        return;
    }
    if (s+mins[l-1] >= ans || v+minv[l-1] > n || (n-v)*2 >= R*(ans-s)) return;
    down(r, R-1, l)
    {
        if (l == m) s = r*r;
        int tmp = min((n-v-minv[l-1])/(r*r), H-1);
        down(h, tmp, l) Search(v+r*r*h, s+2*r*h, l-1, r, h);
    }
}

int main()
{
    scanf("%d%d", &n, &m); ans = n+1;
    rep(i, 1, m) minv[i] = minv[i-1]+i*i*i;
    rep(i, 1, m) mins[i] = mins[i-1]+2*i*i;    
    Search(0, 0, m, sqrt((double)(n-minv[m-1])/m)+1, (n-minv[m-1])/(m*m)+1);
    if (ans == n+1) ans = 0; printf("%d\n", ans);
    return 0;
}