Leetcoder: compute 24

 24点游戏。给你几个数字，判断他们做加减乘除运算是否可以得到24，顺序可以是任意的。dfs搜索搞定。。。但是这里要注意一些细节，每次计算得到新的数之后最好加入数组做下一次搜索，不然容易出错。

public class Solution {

 private boolean compute(int[] nums, int target) {

  boolean[] visit = new boolean[nums.length];

  return helper(nums, visit, target, nums.length);

}

 private boolean helper(int[] nums, boolean[] visit, int target, int c) {

  if (c == 1) {

   for (int i = 0; i < nums.length; i++) {

    if (!visit[i]) {

     return nums[i] == target;

}

}

  } else {

   for (int i = 0; i < nums.length; i++) {

    if (visit[i])

     continue;

    for (int j = i + 1; j < nums.length; j++) {

     if (visit[j])

      continue;

     int n1 = nums[i];

     int n2 = nums[j];

     visit[j] = true;

     nums[i] = n1 + n2;

     if (helper(nums, visit, target, c - 1))

      return true;

     nums[i] = n1 - n2;

     if (helper(nums, visit, target, c - 1))

      return true;

     nums[i] = n2 - n1;

     if (helper(nums, visit, target, c - 1))

      return true;

     nums[i] = n1 * n2;

     if (helper(nums, visit, target, c - 1))

      return true;

     if (n2 != 0) {

      nums[i] = n1 / n2;

      if (helper(nums, visit, target, c - 1))

       return true;

}

     if (n1 != 0) {

      nums[i] = n2 / n1;

      if (helper(nums, visit, target, c - 1))

       return true;

}

     nums[i] = n1;

     visit[j] = false;

}

}

}

  return false;

}

 public static void main(String args[]) {

  Solution s = new Solution();

  System.out.println(s.compute(new int[] { 2, 3, 2, 1 }, 24));

}

}

Leetcoder