LeetCode 16. 3Sum Closest (Two-Pointer)

タイトルの説明
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).
テーマ解析
この問題は15題3 Sumと似ている.まずソートを行い、iが1からcnt-2まで遍歴するように構築する.jとkの構造two-pointer法を用いてleetcode 11題を詳しく紹介する
コード#コード#

class Solution {
public:
    int threeSumClosest(vector<int>& nums, int target) {
        int cnt = nums.size();
        assert(cnt>=3);
        sort(nums.begin(),nums.end());
        int ans = nums[0]+nums[1]+nums[2];
        for(int i = 0;i2;++i)
        {
            if(i>1&&nums[i]==nums[i-1])
            {
                continue;
            }
            int j = i+1,k=cnt-1;   //              
            while(jint sum = nums[i]+nums[j]+nums[k];
                if(abs(sum-target)<abs(ans-target))
                {
                    ans = sum;
                }
                if(sum == target)
                {
                    return target;
                }
                if(sumelse
                {
                    --k;
                }
            }
        }
        return ans;
    }
};