LeetCode——3Sum Closest

Question

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.

For example, given array S = {-1 2 1 -4}, and target = 1.
The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).

Solution

• 先排序，然后遍历每一个元素nums[i]，并且在其之后找nums[j]，nums[k]，j<k，使得结果最接近。

sum = nums[i] + nums[j] + nums[k];
if sum > target k--;
if sum < target j++;
if sum == target return;

Code

class Solution {
public:
    int threeSumClosest(vector<int>& nums, int target) {
        sort(nums.begin(), nums.end());
        int minValue = nums[0] + nums[1] + nums[2];
        int res = abs(minValue - target);
        for (int i = 0; i < nums.size() - 2; i++) {
            int j = i + 1;
            int k = nums.size() - 1;
            while (j < k) {
                int sum = nums[i] + nums[j] + nums[k];
                if (abs(sum - target) < res) {
                    res = abs(sum - target);
                    minValue = sum;
                }
                if (sum > target)
                    k--;
                else if (sum < target)
                    j++;
                else
                    return sum;
            }
        }
        return minValue;
    }
};