剑指 Offer 05. 替换空格（java双指针）

class Solution {
    
 public String replaceSpace(String s) {
    
    if (s == null) return null;

    StringBuilder str = new StringBuilder();

    for (int i = 0; i < s.length(); i++) {
        if (s.charAt(i) == ' ') {
            str.append("  ");//增加两个空格
        }
    }   

    int oldl = s.length()-1;
    s+=str;
    int newl = s.length()-1;
    char[] chars = s.toCharArray();//字符串转换成字符数组

    for (int i = oldl,j = newl; i < j; i--,j--) {
        if (chars[i] != ' ') {
           chars[j] = chars[i]; 
        } else {
            chars[j] = '0';
            chars[j-1] = '2';
            chars[j-2] = '%';
            j = j-2;
        }
    }
    
    return new String(chars);
	
	//错误用法
    // for (int i = oldl,j = newl; i < j; i--,j--) {
    //         if (s.charAt(i) != ' ') {
    //             s.charAt(j) = s.charAt(i);
    //         } else {
    //             s.charAt(j) = '0';
    //             s.charAt(j-1) = '2';
    //             s.charAt(j-2) = '%';
    //             j = j-2;
    //         }
    //     }

    // return s;
 }
}