LeetCode 016 3Sum Closest

题目描述：3Sum Closest

Given an array S of n integers, find three integers in S such that the sum is closest to a given number, target. Return the sum of the three integers. You may assume that each input would have exactly one solution.

    For example, given array S = {-1 2 1 -4}, and target = 1.

    The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).

分析：

和3Sum很像，设一个gap，每次都比较更新gap！

① gap == 0，则返回，因为题目说明只有一个解；

② gap > 0，q--；

③ gap < 0，p++；

④ 直到p == q。

代码如下：

class Solution {
public:
    int threeSumClosest(vector<int> &num, int target) {
        
        int result = 0;
        int min_gap = INT_MAX;
        
        sort(num.begin(), num.end());
        
        for(int i = 0; i < num.size(); i++){
            
            int p = i + 1, q = num.size() - 1;
            
            while(p < q){
                int sum = num[i] + num[p] + num[q];
                int gap = abs(sum - target);
                
                if(gap < min_gap){
                    result = sum;
                    min_gap = gap;
                }
                
                if(sum < target) 
                    p++;
                else 
                    q--;
            }
        }
        
        return result;
        
    }
};

 Java:

    public int threeSumClosest(int[] nums, int target) {

        int result = 0;
        int min_gap = Integer.MAX_VALUE;

        Arrays.sort(nums);

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

            int p = i + 1, q = nums.length - 1;

            while (p < q) {
                int sum = nums[i] + nums[p] + nums[q];
                int gap = Math.abs(sum - target);

                if (gap < min_gap) {
                    min_gap = gap;
                    result = sum;
                }

                if (sum < target) {
                    p++;
                } else {
                    q--;
                }
            }
        }

        return result;
    }