LeetCode(16):3Sum Closest

Posted 2020-06-09

3Sum 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).

题意：给定一个数组和目标元素，找出数组中的3个元素使其和最接近目标元素。

思路：首先对给定的数组进行排序，然后从0到数组元素长度len-2开始循环，对于每层循环，定义两个指针一个left指向i+1,right指向数组的尾部，然后开始判断i,left和start指向的元素之和是否更接近给定的元素，如果接近则更新，然后判断3个元素的和是大于给定的元素还是小于给定的元素，大于的话left指针加1，小于的话right指针减1；

代码：

public int threeSumClosest(int[] nums, int target) {
        int closest = nums[0] + nums[1] + nums[2];
        int diff = Math.abs(closest - target);
        Arrays.sort(nums);
        for (int i = 0; i < nums.length - 2; i++) {
            int start = i + 1;
            int end = nums.length - 1;
            while (start < end) {
                int sum = nums[i] + nums[start] + nums[end];
                int newDiff = Math.abs(sum - target);
                if (newDiff < diff) {
                    diff = newDiff;
                    closest = sum;
                }
                if (sum < target)
                    start++;
                else
                    end--;
            }
        }
        return closest;
    }