数组 -- 3Sum Closet -- 图解

最新推荐文章于 2021-07-02 14:12:25 发布

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本文深入探讨了3SumClosest算法，旨在从给定整数数组中寻找三个数，使其和最接近指定目标值。文章详细介绍了算法的实现过程，包括排序、双指针技巧及如何使用upper_bound和lower_bound函数优化搜索效率。

3Sum Closest
描述
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.
e sum that is closest to the target is 2. (-1 + 2 + 1 = 2).

class Solution{
public:
       int threeSumCloest(vector<int>& num,int target){
            int result = 0;
            int min_gap = INT_MAX;
            sort(num.begin(),num.end());
            for(auto a = num.begin();a !=prev(num.end(),2); a = upper_bound(a,prev(num.end()),*a){
                auto b = next(a);
                auto c = prev(num.end());
                while(b < c){
                    const int sum = *a + *b + *c;
                    const int gap = abs(sum - target);
                    if(gap < min_gap ) {
                        result = sum ;
                        min_gap = gap;
                    }
                    if(sum < target){
                        b = upper_bound(b, c, *b);
                    }
                    else{
                        c = prev(lower_bound(b, c, *c));
                    }       
                }
            }
            return result;
       }
};