3Sum Closest

Problem:
Given an array S of n integers, find three integers in S such that the sum is closest to a given number, target. Return the sum of the three integers. You may assume that each input would have exactly one solution.

Solution:
class Solution {
public:
    int threeSumClosest(vector<int> &num, int target) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
         int i, j, k, sum, diff, clos1, clos2, storedMinDiff, storedMaxDiff;

        vector<vector<int> > solution;
        sort(num.begin(), num.end());
       
        int length = num.size();
        storedMinDiff = target - num[length - 1] - num[length - 2] - num[length - 3];
        storedMaxDiff = target - num[0] - num[1] - num[2];
       
        for (i = 0; i < num.size(); i++) {
            j = i+1;
            k = num.size() - 1;
            while (j < k) {
                sum = num[i] + num[j] + num[k];
                diff = target - sum;

                if (diff == 0) {
                    return sum;
                } else if (diff < 0) {
                    k--;
                    if (diff != max(storedMinDiff, diff))
                        continue;
                    storedMinDiff = diff;
                    // Closest sum in negatives.
                    clos1 = sum;
                } else if (diff > 0) {
                    j++;
                    if (diff != min(storedMaxDiff, diff))
                        continue;
                    storedMaxDiff = diff;
                    // Closest sum in positives.
                    clos2 = sum;
                }

            }

        }
        if (abs(target - clos1) < abs(target - clos2))
            return clos1;
        else
            return clos2;

    }
};