剑指offer面试题 java解答51-55

面试题51：数组中重复的数字

public class Test51 {    public static boolean duplicate(int[] numbers){        boolean found=false;        if (numbers==null||numbers.length<1) {            return found;        }        int length=numbers.length;        for (int i = 0; i < length; i++) {            if (numbers[i]<0||numbers[i]>length-1) {                return found;            }        }        for (int i = 0; i < numbers.length; i++) {            if (numbers[i]!=i) {                if (numbers[i]==numbers[numbers[i]]) {                    System.out.println(numbers[i]);                    found=true;                }                int temp=numbers[i];                numbers[i]=numbers[temp];                numbers[temp]=temp;            }        }        return found;    }    public static void main(String[] args) {        int[] numbers={2,3,1,0,2,5,3};        boolean found=duplicate(numbers);        System.out.println(found);    }}

面试题52：构建乘积数组

public class Test52 {       public static int[] multiply(int[] array1) {          if (array1 == null || array1.length <= 0) {              return null;          }          int[] array2 = new int[array1.length];          array2[0] = 1;          for (int i = 1; i < array1.length; i++) {              array2[i] = array2[i-1] * array1[i-1];          }                 double temp = 1;         for (int i = array1.length-2; i >= 0; i--) {              temp *= array1[i+1];              array2[i]*=temp;        }                   return array2;      }      public static void main(String[] args) {          int[] array1 = {1,2,3,4,5};          int[] array2 = multiply(array1);          for (int i = 0; i < array2.length; i++)              System.out.println(array2[i]);      }   }

面试题53：正则表达式匹配

public class Test53 {    private static boolean matchCore(char[] pPstr,int indexStr,char[] pPattern,int indexPattern){        int strLen=pPstr.length;        int patternLen=pPattern.length;        if (indexStr==strLen&&indexPattern==patternLen) {            return true;        }        if (indexStr!=strLen&&indexPattern==patternLen) {            return false;        }        if (indexPattern<patternLen-1&&pPattern[indexPattern+1]=='*') {            if (pPstr[indexStr]==pPattern[indexPattern]||(pPattern[indexPattern]=='.'&&indexStr!=strLen)) {                return matchCore(pPstr, indexStr+1, pPattern, indexPattern+2)                    || matchCore(pPstr, indexStr+1, pPattern, indexPattern)                    || matchCore(pPstr, indexStr, pPattern, indexPattern+2);            }else {                return matchCore(pPstr, indexStr, pPattern, indexPattern+2);            }        }        if (pPstr[indexStr]==pPattern[indexPattern]||(pPattern[indexPattern]=='.'&&indexStr!=strLen)) {            return matchCore(pPstr, indexStr+1, pPattern, indexPattern+1);        }        return false;    }    public static boolean match(String str,String pattern){        if (str==null||pattern==null) {            return false;        }        char[] pPstr=str.toCharArray();        char[] pPattern=pattern.toCharArray();        return matchCore(pPstr,0,pPattern,0);    }    public static void main(String[] args) {        boolean match=match("aaa", "ab*ac*a");        System.out.println(match);    }}

面试题54：表示数值的字符串

public class Test54 {    public static boolean isNumeric(String string){        if (string==null) {            return false;        }        char[] str=string.toCharArray();        int strLen=str.length;        int index=0;        if (str[index]=='+'||str[index]=='-') {            index++;        }        if (index>=strLen) {            return false;        }        boolean numeric=true;        index=scanDigits(str,index);        if (index<strLen) {            if (str[index]=='.') {                index++;                index=scanDigits(str, index);                if (index<strLen&&(str[index]=='e'||str[index]=='E')) {                    numeric=isExponential(str,index);                }else {                    if (index==strLen) {                        numeric=true;                    }else {                        numeric=false;                    }                }            }else if (str[index]=='e'||str[index]=='E') {                numeric=isExponential(str,index);            }else {                numeric=false;            }        }        return numeric;    }    private static boolean isExponential(char[] str, int index) {        if (str[index]!='e'&&str[index]!='E') {            return false;        }        index++;        if (index<str.length&&(str[index]=='+'||str[index]=='-')) {            index++;        }        if (index>=str.length) {            return false;        }        index=scanDigits(str, index);        return index==str.length?true:false;    }    private static int scanDigits(char[] str, int index) {        while (index<str.length&&str[index]>='0'&&str[index]<='9') {            index++;        }        return index;    }    public static void main(String[] args) {        boolean numeric=isNumeric("12e+5.4");        System.out.println(numeric);    }}

面试题55：字符流中第一个不重复的字符

import java.io.InputStreamReader;import java.util.Scanner;public class Test55 {    private int[] occurrence=new int[256];    int index=0;    public Test55(){        for (int i = 0; i < 256; i++) {            occurrence[i]=-1;        }    }    public void Insert(char ch){        if (occurrence[ch]==-1) {            occurrence[ch]=index;        }else if(occurrence[ch]>=0){            occurrence[ch]=-2;        }        index++;    }    public char FirstAppearingOnce(){        char ch='\0';        int minIndex=Integer.MAX_VALUE;        for (int i = 0; i < 256; i++) {            if (occurrence[i]>=0&&occurrence[i]<minIndex) {                ch=(char)i;                minIndex=occurrence[i];            }        }        return ch;    }    public static void main(String[] args) {        Test55 t=new Test55();        Scanner scanner=new Scanner(System.in);        while (scanner.hasNext()) {            t.Insert(scanner.next().charAt(0));            char ch=t.FirstAppearingOnce();            System.out.println(ch);        }    }}