16. 3Sum Closest

Posted 2020-06-21 蜃利的阴影下

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).

 

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public class Solution {
    public int threeSumClosest(int[] num, int target) {
        if(num == null || num.length<3)
            return 0;
        
        Arrays.sort(num);
        int closest = num[0]+num[1]+num[2];
        for(int first = 0;first<num.length-2;++first)
        {
            if(first > 0 && num[first]==num[first-1])
                continue;
            
            int second = first+1;
            int third = num.length -1;
            
            while(second<third)
            {
                int sum = num[first]+num[second]+num[third]; 
                if(sum == target)
                    return target; 
                if(sum>target)
                    --third;
                else 
                    ++second;
                if(Math.abs(closest-target)>Math.abs(sum-target))
                   closest = sum;
            }
            
        }
        
        return closest;
    }
}