String algorithms (Java implementation)

<1> replace spaces

Title Description

Please implement a function, a string to replace each space to "20%." For example, when the string is We Are Happy. After the string is replaced after We% 20Are% 20Happy.

code show as below:

public class Solution {
    public String replaceSpace(StringBuffer str) {
    	int len = str.length();
        StringBuffer res = new StringBuffer();
        
        for(int i = 0;i < len;i++){
            if(str.charAt(i) != ' '){
                res.append(str.charAt(i));
            }else{
                res.append("%20");
            }
        }
        return res.toString();
    }

 <Two> regular expression matching

Title Description

Implement comprises a function to match '' and '*' regular expression. Mode character '.' Represents any one character '*' indicates that the preceding character can appear any number of times (including 0 time). In this problem, the match is a whole pattern matches all characters of the string. For example, the string "aaa" mode and "aa" and "ab * ac * a" match, but the "aa.a" and "ab * a" do not match.

code show as below:

public class Solution {
    public boolean match(char[] str, char[] pattern) {
        if((null == str && null == pattern) || (null != str && pattern == null)){
            return true;
        }
        
        if(null == str && pattern != null){
            return false;   
        }
        
        return modeoMatch(str,pattern,0,0);
    }
    
    private boolean modeoMatch(char[] str,char[] pattern,int slen,int plen){
        if(slen == str.length && plen == pattern.length){
            return true;
        }
        if(slen != str.length && plen == pattern.length){
            return false;
        }
        
        IF (PLEN +. 1 <pattern.length && pattern [PLEN +. 1] == '*') { 
            IF (sLen <str.length && (STR [sLen] == pattern [PLEN] || pattern [PLEN] == '.')) { 
                return modeoMatch (STR, pattern, sLen +. 1, PLEN) || modeoMatch (STR, pattern, sLen, PLEN + 2); 
                 
            } the else { 
                return modeoMatch (STR, pattern, sLen, PLEN + 2) ; 
            } 
        } 
        
       // must be placed on the back, as determined from the back of the first fishes 
        if (slen <str.length && (str [slen] == pattern [plen] || pattern [plen] ==) '.') { 
            return modeoMatch (STR, pattern, sLen. 1 +, + PLEN. 1); 
        } 
        
        return to false; 
    } 
}

 <Three> represents a numeric string

Title Description

Implement function used to determine whether a string represents a value (including integer and fractional). For example, the string "+100", "5e2", "- 123", "3.1416" and "-1E-16" shows the value. But "12e", "1a3.14", "1.2.3", "+ - 5" and "12e + 4.3" neither.

code show as below:

public class Solution {
    
    private int index = 0;
    public boolean isNumeric(char[] str) {
        if(str.length <= 0){
            return false;
        }
        boolean flag = scanInteger(str);
        if(index < str.length && str[index] == '.'){
            index++;
            flag = scanInteger(str) || flag;
        }
         if(index < str.length && (str[index] == 'E' || str[index] == 'e')){
            index++;
            flag = flag && scanInteger(str);
        }
        return flag && index == str.length;
    that appears{// subtraction symbol behind private Boolean scanInteger (char [] str
    
    }
    
        if(index < str.length && (str[index] == '+' || str[index] == '-')){
            index++;
        }
        int start = index;
        //Character.isDigit(str[index]) 相同与  str[index] >= '0' && str[index] <= '9'
        while(index < str.length && str[index] >= '0' && str[index] <= '9'){
            index++;
        }
        return start < index;
    }
}

 <Four> character stream does not repeat the first character

Title Description

Please implement a function to find the character stream for the first time a character appears only. For example, when the character stream reads only the first two characters "go", the first character only occurs once a "g". When reading out the first six characters "google" from the character stream, first appears only one character is "l".

Output Description:

If the current character stream does not appear there is a character, returns the # character.

code show as below:

 

import java.util.HashMap;
import java.util.ArrayList;

public class Solution {
    
    HashMap<Character,Integer> map = new HashMap<Character,Integer>();
    ArrayList list = new ArrayList();
    
    //Insert one char from stringstream
    public void Insert(char ch) {
        if(!map.containsKey(ch)){
            map.put(ch,1);
            list.add(ch);
        }else{
            map.put(ch,map.get(ch) + 1);
        }
    }
  //return the first appearence once char in current stringstream
    public char FirstAppearingOnce() {
        for(int i = 0;i < list.size();i++){
            if(map.get(list.get(i)) == 1){
                return (char)list.get(i);
            }
        }
        return '#';
    }
}