【473. 火柴拼正方形】深度搜索、划分、回溯

//先求出和为edge的划分。再枚举划分，至多只需要枚举三个划分


import java.util.ArrayList;
import java.util.List;

class Solution {
    int edge = 0;
    List<Integer> stateList = new ArrayList<>();
    int[] matchsticks;

    public static void main(String[] args) {
        Solution solution = new Solution();
        solution.makesquare(new int[]{
                2,2,2,2,2,6
        });
    }

    public boolean makesquare(int[] matchsticks) {
        this.edge = 0;
        for (int u : matchsticks) {
            edge += u;
        }
        if (edge % 4 != 0) {
            return false;
        }
        edge = edge / 4;
        this.matchsticks = matchsticks;
        this.stateList = new ArrayList<>();

        dfs(0, 0, 0);

        int size = stateList.size();
        for (int i = 0; i < size; i++) {
            int statei = stateList.get(i);
            for (int j = i + 1; j < size; j++) {
                int statej = stateList.get(j);
                if ((statei & statej) > 0) {
                    continue;
                }
                for (int k = j + 1; k < size; k++) {
                    int statek = stateList.get(k);
                    if ((statei & statek) > 0 || (statej & statek) > 0) {
                        continue;
                    }
                    return true;
                }
            }
        }
        return false;
    }

    public void dfs(int depth, int sum, int state) {
        if (sum == edge) {
            stateList.add(state);
            return;
        }
        if (sum > edge) {
            return;
        }
        if (depth == matchsticks.length) {
            return;
        }

        dfs(depth + 1, sum, state);
        dfs(depth + 1, sum + this.matchsticks[depth], state | (1 << depth));
    }
}