Leetcode-16最接近的三数之和

我写的

int compare(const void * a, const void * b)
{
    return (*(int *)a - *(int *)b);
}
int threeSumClosest(int* nums, int numsSize, int target) {
    int res;
    int flag1 = 0,flag2 =0;
    int plusAns=0;
    int minusAns =0;
    qsort(nums,numsSize,sizeof(int),compare);
    plusAns = nums[numsSize-1]+nums[numsSize-2]+nums[numsSize-3];
    minusAns = nums[0]+nums[1]+nums[2];
    if(target >0 && plusAns <= 0)
    {
        return plusAns;
    }
    if(target <0 &&minusAns>=0)
    {
        return minusAns;
    }
    plusAns = plusAns -target;
    minusAns = minusAns -target;
    for(int i =0;i<numsSize-2;i++)
    {
        if(i>0&&nums[i]==nums[i-1])continue;
        int start = i+1;
        int end = numsSize-1;

        while(start<end)
        {
            res = nums[i] + nums[start] + nums[end]-target ;

            if(res == 0)
            {
                return res+target;
            }
            else if(res>0)
            {
                flag1 =1;
                end--;
                if(res<=plusAns)
                    plusAns = res;

            }
            else if(res<0)
            {
                flag2 =1;
                start++;
                if(res>=minusAns)
                    minusAns = res;
            }

        }
    }
    int ans;
    if(flag1&&flag2)
    {
        ans = plusAns<=abs(minusAns)?(plusAns+target):(minusAns+target);
    }
    else if(flag1)
    {
        ans = plusAns+target;
    }
    else 
    {
        ans = minusAns+target;
    }
    return ans;
}

别人写的范例

int abs(int tar){
    return tar>0?tar:-tar;
}
void quickSort(int* nums,int first,int end){
    int l=first,r=end;
    if(first>=end)return;
    int temp=nums[l];
    while(l<r){
        while(l<r && nums[r]>=temp)r--;
        if(l<r)nums[l]=nums[r];
        while(l<r && nums[l]<=temp)l++;
        if(l<r)nums[r]=nums[l];
    }
    nums[l]=temp;
    quickSort(nums,first,l-1);
    quickSort(nums,l+1,end);
}
int threeSumClosest(int* nums, int numsSize, int target) {
    int begin,end,i,sum,Min=INT_MAX;
    quickSort(nums,0,numsSize-1);
    for(i=0;i<numsSize-2;i++){
        if(i>0 && nums[i]==nums[i-1])continue;
        begin=i+1;end=numsSize-1;
        while(begin<end){
            sum=nums[i]+nums[begin]+nums[end];
            if(abs(sum-target)<abs(Min))Min=sum-target;
            if(sum==target)return target;
            else if(sum>target)end--;
            else begin++;
        }
    }
    return Min+target;
}

C++版本

class Solution {
public:
    int threeSumClosest(vector<int>& nums, int target) {
        sort(nums.begin(),nums.end());
        int colseSum = nums[0]+nums[1]+nums[2];
        for(int i=0;i<nums.size()-2;i++){
            // 去重，提高速度
            if(i && nums[i]==nums[i-1])continue;
            
            int l = i+1, r = nums.size()-1;
            while(l<r){
                int threeSum = nums[i]+nums[l]+nums[r];
                if(abs(threeSum-target)<abs(colseSum-target))colseSum = threeSum;
                if(threeSum==target)return target;
                if(threeSum>target){
                    // 去重，提高速度
                    if(l<r && nums[r]==nums[r-1])r--;
                    r--;
                }
                else {
                    // 去重，提高速度
                    if(l<r && nums[l]==nums[l+1])l++;
                    l++;
                }
            }
        }
        return colseSum;
    }
};