华为机考

1. 判断回文

public class Huiwen {

    static boolean IsHuiwen(String org){
        StringBuffer strBf = new StringBuffer(org);
        StringBuffer strBfv = strBf.reverse();
        System.out.println("Org:"+org);
        System.out.println("OrgRe:"+strBfv);
        return org.equals(strBfv.toString());  //一定要用org，不能用strBf
    }
    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub

        System.out.println(IsHuiwen("abcba"));
    }

}

2. 求数组中大于平均值的个数

3. 单链表逆置

public class LinkReserve {

    /**
     * @param args
     */
    public static void main(String[] args) {
        // TODO Auto-generated method stub

        class Node{
            String value;
            Node next;
           
            public Node(String value){
                this.value = value;
            }
           
        }
        Node n1 = new Node("a");
        Node n2 = new Node("b");
        Node n3 = new Node("c");
        Node n4 = new Node("d");
        n1.next = n2;
        n2.next = n3;
        n3.next = n4;
       
        Node head = n1;
        Node pre = null;
        Node next = head.next;
        head.next = pre;
       
        while(next != null){
            pre = head;
            head = next;
            next = next.next;
            head.next = pre;
           
        }

        Node p = head;
        while(p != null){
            System.out.println(p.value);
            p = p.next;
        }

    }

}
4. 树的遍历

5. 大数相加

 

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class BigIntegerOperation {


    public static void main(String[] args) throws IOException {

        /**
        * 从控制台读取输入数据 格式为 num1空格num2 为空则exit
        */
        BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
        String str = in.readLine();
        while(str!=null){
        StringTokenizer st = new StringTokenizer(str," ");
        String num1 = st.nextToken();
        String num2 = st.nextToken();
        int len1 = num1.length();
        int len2 = num2.length();
        /**
        * 将不等长的两输入字符串格式化，比如 num1 = 123 num2 = 1234
        * 经格式化后将成为num1 = 0123 num2 = 1234为方便计算
        */
        if(len1 > len2){
            for(int i=0; i< len1-len2; i++){
                num2 = "0"+num2;
            }
        }else if(len2>len1){
            for(int i=0; i< len2-len1; i++){
                num1 = "0"+num1;
            }
        }

        int[] arr1 = BigIntegerOperation.str2intArr(num1);
        int[] arr2 = BigIntegerOperation.str2intArr(num2);

        arr1 = BigIntegerOperation.reverse(arr1);
        arr2 = BigIntegerOperation.reverse(arr2);


        int[] result = BigIntegerOperation.add(arr1, arr2);

//        System.out.print(num1 +" + " + num2 +" = ");
        for(int i=result.length-1; i>=0; i--){
            if(i == result.length-1 && result[i] == 0) continue;
            System.out.print(result[i]);
        }
        str = in.readLine();
        }
    }

    /**
    * 倒置数组元素
    */
    public static int [] reverse(int[] arr){
        int len = arr.length;
        for(int i = 0,j = len-1; i<j; i++,j--){
            int temp = arr[i];
            arr[i] = arr[j];
            arr[j] = temp;
        }
        return arr;
    }

    /**
    *     将字符串转换成整型数组
    */
    public static int [] str2intArr(String str){
        int len = str.length();
        int [] arr = new int[len];
        for(int i = 0 ; i<len; i++){
            arr[i] = str.charAt(i) - '0' ;
        }
        return arr;
    }

    /**
    * 核心方法   两个整型数组相加
    */
    public static int [] add(int a[], int b[]){
        int maxLen = a.length;
        int[] sum = new int[maxLen+1];

        for(int i = 0; i< maxLen ; i++){
            int tempSum = a[i] + b[i];
            sum[i] += tempSum%10;
            int d = tempSum/10; //进位
            sum[i+1] += d;
        }
        return sum;
    }

}