LeetCode 遍历技巧 | 16. 3Sum Closest-优快云博客

本文链接：https://blog.youkuaiyun.com/rical730/article/details/59490360

本文介绍了解决LeetCode 16题——三数之和最接近目标值的一种高效算法实现。该算法通过先排序再使用双指针技巧遍历数组，寻找三个数的组合，使它们的和最接近给定的目标值。

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/*
 * Leetcode16. 3Sum Closest
 * Funtion: 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.
 * Example:
    Input: given array S = {-1 2 1 -4}, and target = 1.
    Output: The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).
    Input:[1,1,1,0]100Expected:3
 * Author: LKJ
 * Date:2016/7/29
 * Hint:related to 15.3Sum
*/
#include <iostream>
#include <vector>
#include <string>
#include <cmath>
#include <algorithm>

using namespace std;



class Solution {
private:
    int myabs(int num){
        if(num < 0) num = -num;
        return num;
    }
public:
    int threeSumClosest(vector<int>& nums, int target) {
        sort(nums.begin(),nums.end());
        int len = nums.size();
        int leftnum;
        int rightnum;
        int sum;
        int diff;
        int temp = 2147483647;
        int ans;

        for(int i = 0; i < len-2; i++){
            leftnum = i+1;
            rightnum = len-1;
            while(leftnum < rightnum){
                sum = nums[i] + nums[leftnum] + nums[rightnum];
                diff = myabs(sum - target);
                if(diff < temp){
                    temp = diff;
                    ans = sum;
                }
                if(sum > target){
                    rightnum--;
                }else{
                    leftnum++;
                }
            }
        }

        return ans;
    }
};

int main(){
    int myarr[4] = {1,1,1,0};
    vector<int> myin1(myarr,myarr+4);
    int myin;
    int myout;
    Solution SA;

    cout << "Please Enter" << endl;
    cin >> myin;
    myout = SA.threeSumClosest(myin1,myin);
    cout << myout << endl;

//    cout<<"VecOUT:"<<myout.size()<<endl;
//    for(unsigned int i = 0; i < myout.size(); i++){
//        for(vector<int>::iterator itt = myout[i].begin() ;itt!=myout[i].end();itt++){
//            cout<<*itt<<"     ";
//        }
//        cout<<endl;
//    }
//    cout<<endl;

    //cout<<"VecOUT:"<<endl;
    //for(vector<int>::iterator it = myout.begin() ;it!=myout.end();it++){
    //    cout<<*it<<"     ";
    //}
    cout<<endl;

    return 0;
}