【剑指Offer 4】替换空格

题目：请实现一个函数，把字符串中的每个空格替换成"%20"，例如“We are happy.”，则输出“We%20are%20happy.”。

Java代码如下：

package demo;

public class TestString {
    public static int replaceBlank(char[] str, int usedLength) {
        if(str == null || str.length < usedLength) {
            return -1;
        }
        int blankNum = 0;
        for(int i = 0; i < usedLength; i++) {
            if(str[i] == ' ') {
                blankNum++;
            }
        }
        if(blankNum == 0) {
            return usedLength;
        }
        int targetLength = usedLength + blankNum * 2;
        int tmp = targetLength;
        if(targetLength > str.length) {
            return -1;
        }
        usedLength--;
        targetLength--;
        while(usedLength >= 0 && usedLength < targetLength) {
            if(str[usedLength] == ' ') {
                str[targetLength--] = '0';
                str[targetLength--] = '2';
                str[targetLength--] = '%';
            } else {
                str[targetLength--] = str[usedLength];
            }
            usedLength--;
        }
        return tmp;
    }

    public static void main(String[] args) {
        char[] str = new char[50];
        str[0] = ' ';
        str[1] = 'h';
        str[2] = 'e';
        str[3] = ' ';
        str[4] = 'l';
        str[5] = 'l';
        str[6] = 'o';
        str[7] = ' ';
        str[8] = ' ';
        str[9] = 'w';
        str[10] = 'o';
        str[11] = 'r';
        str[12] = 'l';
        str[13] = 'd';
        str[14] = ' ';
        str[15] = ' ';
        int targetLength = replaceBlank(str, 16);
        System.out.println(new String(str, 0, targetLength));
    }
}

来源：http://blog.csdn.net/derrantcm/article/details/45330797