蘑菇街2018實習筆試題

前面面試華爲狀態不佳，而後就掛了，華爲不聊技術只聊人生，莫名其妙地沒有進二面，應該是水平不夠吧。等了好久，蘑菇街給了筆試機會。

過久沒有作筆試題了，忽然來了一份筆試，想了好久，兩道題都沒有AC,還不知道有沒有面試機會，暫且記錄一下筆試題吧。都是寶貴的經驗！都是常規題目！

• 重複元素的全排列

基本原理：好比輸入123，則1開頭，對[2,3]全排列，2開頭，對[1,3]全排列，3開頭，對[2,1]全排列。。。如此類推，構成一個樹。數組中全部的值都和第一個值交換後，在對第一個數組後面的數組進行全排列。注意考慮重複元素的情況，先對數組進行排序，若是先後值相同且前一個值被交換過，則跳過當前值。

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);//關鍵
            permute(chars,m+1,n,stringBuilders,booleans);
            swap(chars,i,m);
            booleans[i] = false;
        }
    }
}

• 分糖果問題

基本原理：定義一個全爲1的數組mincandy，先從左往右遍歷rate，若是rate[i]>rate[i-1]，則mincandy[i]=mincandy[i-1]+1，而後從右往左遍歷rate，若是rate[i]>rate[i+1]&&mincandy[i]<mincandy[i+1]+1，則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;
    }
}