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POJ 1020 Anniversary Cake

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This is a simple search problem. With some pruning job it’s sufficient to pass test cases.

The biggest possible area of cake is \(16 \times 10 \times 10\), so the biggest possbile side of cake is \(40\).

Image a cake as a matrix with rows and colums. Each element of this matrix is a 1x1 cell. The problem can be translated to if there exists a method to fill this matrix with squares.

Now fill the matrix in this order: find the lowest leftmost empty cell \(C_{i,j}\). Find successive cells \(C_{i,j}, C_{i, j+1}, \dots, C_{i, j+w}\) with the same height as \(C_{i,j}\).

Choose a square and put it into an area with left upper cell as \(C_{i, j}\). If this can not construct a solution, backtrack to use another squre, otherwise continue to the end and get a solution.

Source code in C++:

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#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;

int s, n;
char cs[11], lens[41];

bool dfs(int x) {
    if (x == n) {
        return true;
    }
    int m = 1, w = 1, suc = 1;
    for (int i = 2; i <= s; ++i) {
        if (lens[i] < lens[m]) {
            m = i, w = 1, suc = 1;
        }
        else if (lens[i] == lens[m] && suc) {
            ++w;
        }
        else {
            suc = 0;
        }
    }

    for (int i = min(10, w); i >= 1; --i) {
        if (cs[i] > 0 && lens[m] + i <= s) {
            cs[i]--;
            for (int j = m; j < m + i; ++j) {
                lens[j] += i;
            }
            if (dfs(x+1)) {
                return true;
            }
            for (int j = m; j < m + i; ++j) {
                lens[j] -= i;
            }
            cs[i]++;
        }
    }
    return false;
}

bool solve() {
    cin >> s >> n;
    memset(cs, 0, sizeof(cs));
    memset(lens, 0, sizeof(lens));

    int sum = 0, tmp;
    for (int i = 0; i < n; ++i) {
        cin >> tmp;
        cs[tmp]++;
        sum += tmp*tmp;
    }
    if (sum != s*s) {
        return false;
    }
    return dfs(0);
}

int main() {
    int t;
    cin >> t;
    while(t--) {
        if (solve()) {
            cout << "KHOOOOB!" << endl;
        }
        else {
            cout << "HUTUTU!" << endl;
        }
    }
}

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