Birthday cake POJ1190

Birthday cake POJ1190

Thinking

Casual working in this: POJ1190
depth-first search, and more pruning shears

ac Code

#include<cstdio>
#include<algorithm>
#include<iostream>
#include<cmath>
#define inf 0x3f3f3f3f
using namespace std;
int N, M, S = inf;
int v = 0, s = 0;
int r[21] = { inf }, h[21] = { inf };
int mins[22], minv[22];
void dfs(int i) {
	if (i == M + 1) {
		if(v==N)
			S = min(S, s);
		return;
	}
	if (v + minv[M - i + 1] > N || s + mins[M - i + 1] >= S) {
		return;
	}
	if (i != 1 && s + 2 * (N - v) / r[i - 1] > S)
		return;
	for (r[i] = min(r[i - 1] - 1, int(sqrt(double(N - v)))); r[i] >= M - i + 1; r[i]--) {
		for (h[i] = min(h[i - 1] - 1, (N - v) / (r[i] * r[i])); h[i] >= M - i + 1; h[i]--) {
			if (i == 1)
				s = r[i] * r[i];
			s += 2 * r[i] * h[i];
			v += r[i] * r[i] * h[i];
			dfs(i + 1);
			s -= 2 * r[i] * h[i];
			v -= r[i] * r[i] * h[i];
		}
	}
}
int main() {
	cin >> N >> M;
	for (int i = 1; i <= M; i++) {
		mins[i] = mins[i - 1] + 2 * i * i;
		minv[i] = minv[i - 1] + i * i * i;
	}
	dfs(1);
	if (S != 0x3f3f3f3f)
		cout << S;
	else
		cout << '0';
}