LeetCode: 4Sum

跟3sum和3sum closest差不多

C++：

class Solution {
 public:
     vector<vector<int> > fourSum(vector<int> &num, int target) {
         // Start typing your C/C++ solution below
         // DO NOT write int main() function
         vector<vector<int>> ret;
         if (num.size() < 4) return ret;
         sort(num.begin(), num.end());
         for (int i = 0; i < num.size()-3; i++) {
             if (i > 0 && num[i] == num[i-1]) continue;
             for (int j = i+1; j < num.size()-2; j++) {
                 if (j > i+1 && num[j] == num[j-1]) continue;
                 int end = num.size()-1;
                 for (int beg = j+1; beg < end; beg++) {
                     if (beg > j+1 && num[beg] == num[beg-1]) continue;
                     int sum = num[i] + num[j] + num[beg] + num[end];
                     if (sum == target) {
                         vector<int> tmp;
                         tmp.push_back(num[i]);
                         tmp.push_back(num[j]);
                         tmp.push_back(num[beg]);
                         tmp.push_back(num[end]);
                         ret.push_back(tmp);
                     }
                     else if (sum > target) end--, beg--;
                 }
             }
         }
         return ret;
     }
 };

java:

public class Solution {
    public List<List<Integer>> fourSum(int[] nums, int target) {
        List<List<Integer>> ans = new ArrayList<List<Integer>>();
        Arrays.sort(nums);
        for (int i = 0; i < nums.length; i++) 
        {
            if (i > 0 && nums[i] == nums[i-1]) continue;
            for (int j = i+1; j < nums.length; j++)
            {
                if (j > i+1 && nums[j] == nums[j-1]) continue;
                int left = j+1;
                int right = nums.length-1;
                while (left < right)
                {
                    if (left > j+1 && nums[left] == nums[left-1]) {
                        left++;
                        continue;
                    }
                    int sum = nums[i] + nums[j] + nums[left] + nums[right];
                    if (sum == target) {
                        List<Integer> tmp = new ArrayList<Integer>();
                        tmp.add(nums[i]);
                        tmp.add(nums[j]);
                        tmp.add(nums[left]);
                        tmp.add(nums[right]);
                        ans.add(tmp);
                        left++;
                    }
                    else if (sum < target) left++;
                    else right--;
                }
            }
        }
        return ans;
    }
}