Java implements ideas and codes for replacing spaces in strings

Problem description:

Please implement a function to replace spaces in a string with "%20". For example, when the string is We Are Happy., the replaced string is We%20Are%20Happy.

Basic idea of ​​​​replacing spaces in strings in java:

Replace in reverse order to reduce time complexity

Implementation plan:

• StringOnce initialized, it cannot be changed.

• Use StringBuffer because of Niuke.com’s template.

• In actual use, it is recommended to use StringBuilder for single threads because it is lock-free and highly efficient.

• In multi-threading, use StringBuffer.

• The built-in functions of both are the same

Thinking:

• Change the original string or create a new string (if it is original, you need to reset the length setLength())

• Do not consider using the existing replace()

Java implements the code to replace spaces in a string:

public static String replaceSpace(StringBuffer str){        
        int length = str.length();        int spacenum = 0;        
        //统计空格字符个数
        for(int i=0;i<length;i++){            if(str.charAt(i) == &#39; &#39;)
                spacenum++;
        }        
        int lengthNew = length + spacenum*2;
        str.setLength(lengthNew);        int index = length-1;        int indexNew = lengthNew-1;        for(;index>=0;index--){            
            if(str.charAt(index) == &#39; &#39;){
                str.setCharAt(indexNew--, &#39;0&#39;);
                str.setCharAt(indexNew--, &#39;2&#39;);
                str.setCharAt(indexNew--, &#39;%&#39;);
            }            else{
                str.setCharAt(indexNew--, str.charAt(index));
            }
        }        return str.toString();
    }

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