473.cpp

// dfs.cpp
class Solution {
  bool can = 0;
  int average;
  int a = 0, b = 0, c = 0, d = 0;

public:
  bool makesquare(vector<int> &nums) {
    int sum = accumulate(nums.begin(), nums.end(), 0);
    if (sum % 4 || nums.size() == 0)
      return 0;
    sort(nums.begin(), nums.end(), greater<int>());
    average = sum / 4;
    if (nums[0] > average)
      return 0;
    dfs(nums, 0);
    return can;
  }
  void dfs(vector<int> &nums, int i) {
    if (d == average & a == b && b == c && c == d) {
      can = 1;
      return;
    }
    if (i == nums.size() || a > average || b > average || c > average ||
        d > average || can)
      return;
    a += nums[i];
    dfs(nums, i + 1);
    a -= nums[i];
    b += nums[i];
    dfs(nums, i + 1);
    b -= nums[i];
    c += nums[i];
    dfs(nums, i + 1);
    c -= nums[i];
    d += nums[i];
    dfs(nums, i + 1);
    d -= nums[i];
  }
};