LeetCode 3Sum Closest

class Solution {
public:
    int threeSumClosest(vector<int> &num, int target) {
        int len = num.size();
        if (len < 3) {
            return 0;
        }
        sort(num.begin(), num.end());
        
        int sum = num[0] + num[1] + num[2];
        for (int i=0; i<len-2; i++) {
            int p = i + 1;
            int q = len - 1;
            while (p < q) {
                int csum = num[i] + num[p] + num[q];
                if (abs(target - csum) < abs(target - sum)) {
                    sum = csum;
                }
                if (csum > target) {
                    q--;
                } else if (csum < target) {
                    p++;
                } else {
                    return csum;
                }
            }
        }
        return sum;
    }
};