public class Solution {
    public String replaceSpace(StringBuffer str) {   
        /*
            思路一：return str.toString().replace(" ", "%20");
            思路二：計算字串的空格數量，空出對應的位置依次插入'%''2''0'三個字元
        */ 	        
        char c[] = new char[str.length()];
    	int count = 0;    	
    	for(int i=0;i<c.length;i++) {
    		c[i] = str.charAt(i);
    		if(c[i]==' ') {    			
    			count++;
    		}    		
    	}
    	char chr[] = new char[c.length+count*2];     	
    	for(int i = 0,j = 0;i<c.length&&j<chr.length;) {
    		if(c[i]==' ') {       			
    			chr[j++] = '%';
    			chr[j++] = '2';
    			chr[j++] = '0';
    		}
    		else {
    			chr[j] = c[i];     			
    			j++;
    		}
    		i++;
    	}	
        /*
            toString方法出現亂碼？!
            return chr.toString();  // [
 
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    	*/
    	return String.valueOf(chr);
    }
}