剑指Offer 面试题03. 数组中重复的数字

import java.text.SimpleDateFormat;
import java.util.*;

/**
 * @Auther: truedei
 * @Date: 2020 /20-5-6 22:46
 * @Description:
 */
public class TestA {

    static  public int findRepeatNumber(int[] nums) {

        //702895纳秒
        Arrays.sort(nums);
        for (int i = 0; i < nums.length; i++) {
            if(nums[i] == nums[i+1]){
                return nums[i];
            }
        }
        return -1;



        //371202纳秒
        for (int i = 0; i < nums.length ; i++) {
            for (int j = 0; j <nums.length ; j++) {
                if(nums[i]==nums[j]){
                    return nums[i];
                }
            }
        }
        return -1;


        //381036纳秒
        Set<Integer> set = new HashSet<>();
        for (int i = 0; i < nums.length ; i++) {

            final boolean add = set.add(nums[i]);//如果未包含会返回true

            if(!add){
                return nums[i];
            }
        }
        return -1;



        //443464纳秒
        Map<Integer,Integer> maps = new HashMap<>();
        for (int i = 0; i < nums.length; i++) {
            boolean b = maps.containsKey(nums[i]);//如果已经包含了主键，就返回true
            if(!b){
                return nums[i];
            }else{
                maps.put(nums[i],maps.get(nums[i]));
            }
        }
        return -1;
    }

    public static void main(String[] args) {

        Long starTime = System.nanoTime(); // 纳秒

        System.out.println(findRepeatNumber(new int[]{2, 3, 1, 0, 2, 5, 3}));

        Long endTime = System.nanoTime() ; // 纳秒
        
        System.out.println("+=用时："+(endTime - starTime)+"纳秒");

    }
}