前面面试华为状态不佳,然后就挂了,华为不聊技术只聊人生,莫名其妙地没有进二面,应该是水平不够吧。等了很久,蘑菇街给了笔试机会。
太久没有做笔试题了,突然来了一份笔试,想了很久,两道题都没有AC,还不知道有没有面试机会,暂且记录一下笔试题吧。都是宝贵的经验!都是常规题目!
- 重复元素的全排列
基本原理:比如输入123,则1开头,对[2,3]全排列,2开头,对[1,3]全排列,3开头,对[2,1]全排列。。。如此类推,构成一个树。数组中所有的值都和第一个值交换后,在对第一个数组后面的数组进行全排列。注意考虑重复元素的状况,先对数组进行排序,如果前后值相同且前一个值被交换过,则跳过当前值。
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Scanner;
public class NoPermutation{
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
String s = scanner.nextLine();
char[] chars = s.toCharArray();
//char[] chars = new char[]{'a','c','c'};
Arrays.sort(chars);
boolean[] booleans = new boolean[chars.length];
List<StringBuilder> stringBuilders = new ArrayList<>();
permute(chars,0,chars.length,stringBuilders,booleans);
System.out.print(stringBuilders.toString());
}
public static void swap(char[] chars,int i,int j){
char temp = chars[i];
chars[i] = chars[j];
chars[j] = temp;
}
public static void permute(char[] chars,int m,int n,List<StringBuilder> stringBuilders,boolean[] booleans){
if (m==n){
StringBuilder stringBuilder = new StringBuilder();
for (int i = 0; i < n; i++) {
stringBuilder.append(chars[i]);
}
stringBuilders.add(stringBuilder);
return;
}
for (int i = m; i < n; i++) {
if (i>0&&chars[i]==chars[i-1]&&!booleans[i-1]) continue;
booleans[i] = true;
swap(chars,i,m);//关键
permute(chars,m+1,n,stringBuilders,booleans);
swap(chars,i,m);
booleans[i] = false;
}
}
}
- 分糖果问题
基本原理:定义一个全为1的数组mincandy,先从左往右遍历rate,如果rate[i]>rate[i-1],则mincandy[i]=mincandy[i-1]+1,然后从右往左遍历rate,如果rate[i]>rate[i+1]&&mincandy[i]<mincandy[i+1]+1,则mincandy[i] = mincandy[i+1]+1。
import java.util.Arrays;
import java.util.Scanner;
public class Candy {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
String in = scanner.nextLine();
String[] ratings = in.split(" ");
System.out.print(mincandy(ratings));
}
public static int mincandy(String[] ratings){
int[] rates = new int[ratings.length];
for (int i = 0; i < ratings.length; i++) {
rates[i] = Integer.parseInt(ratings[i]);
}
int[] mincandy = new int[ratings.length];
Arrays.fill(mincandy,1);
for (int i = 1; i < ratings.length; i++) {
if (rates[i]>rates[i-1]){
mincandy[i] = mincandy[i-1]+1;
}
}
int sum = mincandy[rates.length-1];
for (int i = rates.length-2; i >= 0 ; i--) {
if (rates[i]>rates[i+1]&&mincandy[i]<mincandy[i+1]+1){
mincandy[i] = mincandy[i+1]+1;
}
sum+=mincandy[i];
}
return sum;
}
}