LeetCode—— 最接近的三数之和

题目地址：https://leetcode-cn.com/problems/3sum-closest/

解题思路：和上一题三数之和类似（https://www.cnblogs.com/cc-xiao5/p/13392624.html），唯一的区别就是通过差的绝对值判断最接近

class Solution {
public:
    int threeSumClosest(vector<int>& nums, int target) {
        int pa, pb, pc;//三个指针，代表三个数的位置
        int len = nums.size();
        int ans, tmp;
        sort(nums.begin(), nums.end());
        ans = nums[0] + nums[1] + nums[2];
        for (pa = 0; pa < len; pa++) {
            pc = len - 1;
            if (pa > 0 && nums[pa] == nums[pa - 1])
                continue;
            for (pb = pa + 1; pb < len && pb < pc; pb++) {
                if (pb > pa + 1 && nums[pb] == nums[pb - 1])
                    continue;
                tmp = nums[pa] + nums[pb] + nums[pc];
                while (pb < pc&&tmp> target) { //pc左移，使得总和变小
                    pc--;
                    if (pb < pc)
                        tmp = nums[pa] + nums[pb] + nums[pc];
                    ans = abs(ans - target) > abs(tmp - target) ? tmp : ans;
                }
                if (tmp < target)//pb右移，使得总和变大
                    ans = abs(ans - target) > abs(tmp - target) ? tmp : ans;
                else if (tmp == target)
                    return target;
            }        
        }
        return ans;
    }
};