题目：

题解：

class Solution {
    public boolean makesquare(int[] matchsticks) {
        int totalLen = Arrays.stream(matchsticks).sum();
        if (totalLen % 4 != 0) {
            return false;
        }
        int len = totalLen / 4, n = matchsticks.length;
        int[] dp = new int[1 << n];
        Arrays.fill(dp, -1);
        dp[0] = 0;
        for (int s = 1; s < (1 << n); s++) {
            for (int k = 0; k < n; k++) {
                if ((s & (1 << k)) == 0) {
                    continue;
                }
                int s1 = s & ~(1 << k);
                if (dp[s1] >= 0 && dp[s1] + matchsticks[k] <= len) {
                    dp[s] = (dp[s1] + matchsticks[k]) % len;
                    break;
                }
            }
        }
        return dp[(1 << n) - 1] == 0;
    }
}