求数组三项之和最接近某个目标数字

描述

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).

思路

1、排序数组

2、循环遍历数组，两面夹逼

空间复杂度O(1)，时间复杂度O(n2)

代码

package com.lilei.spring_boot_db.boot.pack1115;

import java.util.Arrays;

public class sum3closest {

	public static void main(String[] args) {

		int[] array = new int[]{1,2,3,4,5,6,7,9};
		
		System.out.println(sum(array,25));
	}

	static int sum(int[] array, int target) {
		int result = Integer.MIN_VALUE;

		Arrays.sort(array);

		for (int i = 0; i < array.length; i++) {

			int left = 0;
			int right = array.length - 1;

			while (left < right) {
				if (left != i && right != i) {
					if (Math.abs(target - result) > Math.abs(target
							- (array[left] + array[i] + array[right])))
						result = array[left] + array[i] + array[right];

					if (array[left] + array[i] + array[right] < target) {
						left++;
					} else if (array[left] + array[i] + array[right] > target) {
						right--;
					} else {
						return array[left] + array[i] + array[right];
					}
				} else if (left == i)
					left++;
				else
					right--;
			}

		}

		return result;
	}

}