16_3SumClosest.java

/*
 * 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).
 * 
 */


public class Solution {
    public int threeSumClosest(int[] num, int target) {
        Arrays.sort(num);
        int result = num[0] + num[1] + num[num.length - 1];
        for(int i=0; i<num.length-2; i++) {
            int start = i + 1;
            int end = num.length - 1;
            while(start < end) {
                int threeSum = num[i] + num[start] + num[end];
                if(threeSum == target) return target;
                else if(threeSum < target) start++;
                else if(threeSum > target) end--;
                if(Math.abs(threeSum - target) < Math.abs(result - target))
                result = threeSum;
            }
        }
        return result;
    }
}