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ThreeSumClosest.java
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ThreeSumClosest.java
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package com.hncboy;
import java.util.Arrays;
/**
* @author hncboy
* @date 2019/9/30 8:59
* @description 16.最接近的三数之和
*
* 定一个包括 n 个整数的数组 nums 和 一个目标值 target。
* 找出 nums 中的三个整数,使得它们的和与 target 最接近。返回这三个数的和。假定每组输入只存在唯一答案。
* 例如,给定数组 nums = [-1,2,1,-4], 和 target = 1.
* 与 target 最接近的三个数的和为 2. (-1 + 2 + 1 = 2).
*/
public class ThreeSumClosest {
public static void main(String[] args) {
int[] nums = new int[]{1, 1, 1, 0};
System.out.println(new ThreeSumClosest().threeSumClosest2(nums, -100));
}
/**
* 双指针
*
* @param nums
* @param target
* @return
*/
private int threeSumClosest2(int[] nums, int target) {
Arrays.sort(nums);
int min = nums[0] + nums[1] + nums[2];
int left;
int right;
for (int i = 0; i < nums.length; i++) {
left = i + 1;
right = nums.length - 1;
// 区间的最小值
int rangeMin = nums[i] + nums[left] + nums[left + 1];
// 区间的最大值
int rangeMax = nums[right - 2] + nums[right - 1] + nums[right];
// target < rangeMin || target > rangeMax 只需比较两个值
if (rangeMin > target) {
if (rangeMin - target < Math.abs(min - target)) {
min = rangeMin;
}
} else if (rangeMax < target) {
if (target - rangeMax < Math.abs(min - target)) {
min = rangeMax;
}
} else {
// target 在区间内则根据比较大小进行左右指针的移动
while (left < right) {
int sum = nums[i] + nums[left] + nums[right];
if (Math.abs(target - sum) < Math.abs(target - min)) {
min = sum;
}
if (sum > target) {
right--;
} else if (sum < target) {
left++;
} else {
return min;
}
}
}
}
return min;
}
/**
* 暴力
*
* @param nums
* @param target
* @return
*/
private int threeSumClosest1(int[] nums, int target) {
int length = nums.length;
long min = Integer.MIN_VALUE;
for (int i = 0; i < length; i++) {
for (int j = i + 1; j < length; j++) {
for (int k = j + 1; k < length; k++) {
if (Math.abs(min - target) > Math.abs(nums[i] + nums[j] + nums[k] - target)) {
min = nums[i] + nums[j] + nums[k];
if (min == target) {
return (int) min;
}
}
}
}
}
return (int) min;
}
}