优化一下

class Solution {
public:
    int threeSumClosest(vector<int>& nums, int target) {
        sort(begin(nums), end(nums));
        int ans=nums[0]+nums[1]+nums[2];
        int L=0,R=0,sum=0,min=0,max=0;
        for (int i = 0; i < nums.size(); i++) {
            L=i+1;R=nums.size()-1;
            if(i>0&&nums[i]==nums[i-1]) continue;   //对i去重
            while(L<R) {
                min=nums[i]+nums[L]+nums[L+1];
                if(target<min&&abs(min-target)<abs(ans-target)) {
                    ans=min; break;
                }
                max=nums[i]+nums[R]+nums[R-1];
                if(target>max&&abs(max-target)<abs(ans-target)) {
                    ans=max; break;
                }
                sum=nums[i]+nums[L]+nums[R];
                if(sum==target) return sum;
                else if(sum>target) {
                    R--;
                    while(L<R&&nums[R]==nums[R+1]) R--; //对L去重
                }
                else {
                    L++;
                    while(L<R&&nums[L]==nums[L-1]) L++; //对R去重
                };
                if(abs(sum-target)<abs(ans-target)) ans=sum;
            }
        }
        return ans;

    }
};