[JZ2 替换空格]

1. 直接调用库函数

   public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param s string字符串 
     * @return string字符串
     */
    public String replaceSpace (String s) {
        return s.replaceAll(" ","%20");
    }
   }

2. 逐个遍历

   import java.util.*;
   public class Solution {
     /**
      * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
      *
      * 
      * @param s string字符串 
      * @return string字符串
      */
     public String replaceSpace (String s) {
         StringBuilder sb = new StringBuilder();
         char []chars = s.toCharArray();
         for(int i=0;i<chars.length;i++){
             if (chars[i] ==' ')
                 sb.append("%20");
             else sb.append(chars[i]);
         }
         return sb.toString();
     }
   }

class Solution {
    public String replaceSpace(String s) {
        char []str = new char[s.length()*3];
        int size = 0;
        for (int i=0;i<s.length();i++){
            char c = s.charAt(i);
            if (c == ' '){
                str[size++] = '%';
                str[size++] = '2';
                str[size++] = '0';
            }
            else str[size++] = c;
        }
        String newStr = new String(str,0,size);
        return newStr;
    }
}