题目描述
在一个长度为n的数组里的所有数字都在0到n-1的范围内。 数组中某些数字是重复的，但不知道有几个数字是重复的。也不知道每个数字重复几次。请找出数组中任意一个重复的数字。 例如，如果输入长度为7的数组{2,3,1,0,2,5,3}，那么对应的输出是第一个重复的数字2。
方法一：利用HashSet的contains的唯一性。
package test;
import java.util.HashSet;
import java.util.Set;
//dupliacation(尤指不必要时)重复
class Solution {//{2,3,1,0,2,5,3}// Parameters:// numbers: an array of integers// length: the length of array numbers// duplication: (Output) the duplicated number in the array number,length of duplication array is 1,so using duplication[0] = ? in implementation;// Here duplication like pointor in C/C++, duplication[0] equal *duplication in C/C++// 这里要特别注意~返回任意重复的一个，赋值duplication[0]// Return value: true if the input is valid, and there are some duplications in the array number// otherwise falsepublic boolean duplicate(int[] numbers,int length,int[] duplication) {Set<Integer> set = new HashSet<>();for(int i =0 ;i<length;i++){if(set.contains(numbers[i])){duplication[0] = numbers[i];return true;}else{set.add(numbers[i]);}}return false;}
}
public class Main{public static void main(String[] args) {int[] a = {2,3,1,0,2,5,3};int length = a.length;int[] duplication = new int[1];//数组长度是1，而不是0，0就没有长度了Solution p = new Solution();boolean c = p.duplicate(a, length, duplication);System.out.println("结果："+c);}
}
方法二：使用boolean类型的数组，利用boolean只占一位，所以还是比较省的
package test;
class Solution {//{2,3,1,0,2,5,3}// Parameters:// numbers: an array of integers// length: the length of array numbers// duplication: (Output) the duplicated number in the array number,length of duplication array is 1,so using duplication[0] = ? in implementation;// Here duplication like pointor in C/C++, duplication[0] equal *duplication in C/C++// 这里要特别注意~返回任意重复的一个，赋值duplication[0]// Return value: true if the input is valid, and there are some duplications in the array number// otherwise falsepublic boolean duplicate(int[] numbers, int length, int[] duplication) {boolean[] k = new boolean[length];//Boolean类型的变量，默认是falsefor (int i = 0; i < k.length; i++) {if (k[numbers[i]]) {duplication[0] = numbers[i];return true;}k[numbers[i]] = true;}return false;}
}
public class Main{public static void main(String[] args) {int[] a = {2,3,1,0,2,5,3};int length = a.length;int[] duplication = new int[1];//数组长度是1，而不是0，0就没有长度了Solution p = new Solution();boolean c = p.duplicate(a, length, duplication);System.out.println("结果："+c);}
}