剑指offer 第二章

1 数据结构
1.1 数组

面试题3：在一个二维数组中，每一行都按照从左往右递增的顺序排列，每一列都按照从上到下递增的顺序排列。请完成一个函数，输入这样的一个二维数组和整数，判断数组中是否存在该整数。

public class FindElement {    public static void main(String[] args) {        int [][] arr ={{1,2,8,9},{2,4,9,12},{4,7,10,13},{6,8,11,15}};        System.out.println(search(arr,7));    }    private static boolean search(int[][] arr, int value) {        int a = arr[0].length;        int b = arr.length;        int i = 0;//行数        int j = a-1;//列数        while (i<=b-1&&j>=0){            if(arr[i][j] == value){                return true;            }            if(arr[i][j]>value){                j--;            }else{                i++;            }        }               return false;    }}

1.2 字符串
　　面试题4：替换空格
　　请实现一个函数，把字符串中的每个空格替换成“%20”。例如输入“we are happy.”，则输出“we%20are%20happy.”

import java.util.Scanner;public class ReplaceBlank {    public static String replace1(String str){        String str1 = new String(str);        return str1.replace(" ", "%20");    }    public static String replace2(String str){        String str1 = new String(str);        char[] charArr = str1.toCharArray();        int originalLength = charArr.length;        int count = 0;        for (int i=0;i<charArr.length;i++){            char item = charArr[i];            if (item == ' '){                count++;            }                   }        int newLength = originalLength + count*2;        char[] newcharArr = new char[newLength];        int indexOfOriginal = originalLength-1;        int indexOfNew = newLength-1;        while (indexOfOriginal >= 0){            if (charArr[indexOfOriginal] == ' '){                newcharArr[indexOfNew--] = '0';                newcharArr[indexOfNew--] = '2';                newcharArr[indexOfNew--] = '%';                indexOfOriginal--;            } else{                newcharArr[indexOfNew--] = charArr[indexOfOriginal--];            }        }        return String.valueOf(newcharArr);    }    public static void main(String[] args) {        Scanner sc = new Scanner(System.in);        String s0 = sc.nextLine();        System.out.println(replace1(s0));        System.out.println(replace2(s0));    }}

1.3 链表
　　链表的空间效率比数组高，但时间效率O(n)比数组O(1)低。
　　
面试题6：输入一个链表的头节点，从尾到头反过来打印每个节点的值。

import java.util.Stack;public class No5PrintListNodeReverse {    public static void main(String[] args) {        ListNode head = new ListNode(0);        ListNode node_1 = new ListNode(1);        ListNode node_2 = new ListNode(2);        ListNode node_3 = new ListNode(3);        ListNode node_4 = new ListNode(4);        head.setNext(node_1);        node_1.setNext(node_2);        node_2.setNext(node_3);        node_3.setNext(node_4);        node_4.setNext(null);        System.out.println("第一种方式：递归实现");        printListReverse_1(head);        System.out.println();        System.out.println("第二种方式：栈结构实现");        printListReverse_2(head);    }    //用递归实现    private static void printListReverse_1(ListNode head) {        if (head != null){            if(head.getNext() != null){                printListReverse_1(head.getNext());            }            System.out.print(head.getValue() + " ");        }    }    //用栈实现    private static void printListReverse_2(ListNode head){        Stack<Integer> s = new Stack<Integer>();        ListNode p = head;        //进栈        while (p != null){            //每经过一个结点，把节点放到一个栈中            s.push(p.getValue());            p = p.getNext();        }        //出栈        while (!s.isEmpty()){            //遍历完整个链表以后，从栈顶开始逐个输出结点的值            System.out.print(s.pop()+" ");        }        System.out.println();    }}class ListNode{    private int value;    private ListNode next;    public ListNode(int value){        this.value = value;    }    public ListNode(int value, ListNode next){        this.value = value;        this.next = next;    }    public void setValue(int value){        this.value = value;    }    public void setNext(ListNode next){        this.next = next;    }    public int getValue(){        return this.value;    }    public ListNode getNext(){        return this.next;    }}