leetcode-16-数组题-最接近的三数之和

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题目

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解法

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// 排序 + 双指针

class Solution {
public:
    void changePosAdd(int &pos, vector<int>& nums, int n){
        while((pos + 1 < n) && (nums[pos + 1] == nums[pos]))
            ++pos;
        ++pos;
    }

    void changePosSub(int &pos, vector<int>& nums){
        while((pos - 1 > 0) && (nums[pos - 1] == nums[pos]))
            --pos;
        --pos;
    }

    int threeSumClosest(vector<int>& nums, int target) {
        int n = nums.size();
        if (n < 3)
            throw "the size of nums must bigger than 3";
        
        sort(nums.begin(), nums.end());
        int diff = 32765;
        int res;
        int now = 0;
        while(now < n-2){
            int low = now + 1;
            int high = n - 1;
            while(low < high){
                int tempSum = nums[now] + nums[low] + nums[high];
                int tempDiff = tempSum - target;
                if(abs(tempDiff) < diff){
                    diff = abs(tempDiff);
                    res = tempSum;
                }
                if(tempDiff == 0){
                    return res;
                }else if(tempDiff > 0){
                    changePosSub(high, nums);
                }else{
                    changePosAdd(low, nums, n);
                }
            }

            changePosAdd(now, nums, n);
        }

        return res;
    }
};