leetcode : 3 sum closest

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).

tag : two pointers

备注：

int closest = Integer.MAX_VALUE / 2;  否则，当全是负数时，容易溢出。

public class Solution {
    /* (1) 排序
       (2) 把所有三数之和临时存起来，取绝对值最小的，一旦等于0就可以直接返回了。
    */
    public int threeSumClosest(int[] nums, int target) {
        
        int closest = Integer.MAX_VALUE / 2;
        
        if(nums == null || nums.length < 3 ) {
            return closest;
        }
        
        Arrays.sort(nums);
        
        for(int i = 0; i < nums.length - 2; i++) {
            int x = nums[i];
            int left = i + 1;
            int right = nums.length - 1;
            
            while(left < right) {
                int y = nums[left];
                int z = nums[right];
                int sum = x + y + z;
                if(sum - target == 0) {
                   return sum;
                 } 
                if(Math.abs(sum - target) < Math.abs(closest-target)) {
                    closest = sum;
                }
                if(sum < target) {
                    left++;
                } else {
                    right--;
                }
            }
        }
        
        return closest;
      
    }
}