[leetcode] 4sum

与3sum类似，这里直接定代码，需要流量为了提高效果而做的剪枝。

class Solution {
public:
    vector<vector<int>> fourSum(vector<int>& nums, int target) {
        vector<vector<int> > result;
        if (nums.size()<4) return result;
        sort(nums.begin(), nums.end());
        for(size_t i=0;i<nums.size()-3;i++) {
            if (i>0 && nums[i]==nums[i-1]) continue;
            for (size_t j=i+1;j<nums.size()-2;j++){
                if (j-i>=2 && nums[j]==nums[j-1]) continue;
                int cur_target = target-nums[i];
                    int inner_target = cur_target-nums[j];
                    int left_pt = j+1, right_pt = nums.size()-1;
                    while (left_pt < right_pt) {

                        if (nums[left_pt] + nums[right_pt] > inner_target) {
                            right_pt--;
                        } else if (nums[left_pt] + nums[right_pt] < inner_target) {
                            left_pt++;
                        } else {
                            vector<int> temp;
                            temp.push_back(nums[i]);
                            temp.push_back(nums[j]);
                            temp.push_back(nums[left_pt]);
                            temp.push_back(nums[right_pt]);
                            result.push_back(temp);
                            //cout<<nums[i]<<" "<<nums[j]<<" "<<nums[left_pt]<<" "<<nums[right_pt]<<endl;
                            left_pt++;
                            right_pt--;
                            while (left_pt<right_pt && nums[left_pt]== nums[left_pt-1]) {
                                left_pt++;
                            }
                            while(left_pt<right_pt && nums[right_pt] == nums[right_pt+2]) {
                                right_pt--;
                            }
                        }

                    }
            }
        }
        return result;
    }
};