面试题5：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，输入“We are happy.”，则输出“We%20are%20happy.”。
思路：准备两个指针P1和P2，P1指向原始字符串的末尾，P2指向替换之后的字符串的末尾，逐个把P1指定的字符移动到P2上
解决方案：

public class Question5 {
    // length为字符数组string的总容量
    public static void ReplaceBlank(char[] string, int length){
        if (string == null || length <= 0) return;
        // orignalLength为字符串string的实际长度
        int originalLength = 0;
        int numberOfBlank = 0;
        int i = 0;
        while (string[i] != '\u0000'){
            ++originalLength;
            if (string[i] == ' ') ++numberOfBlank;
            ++i;
        }
        // newLength为把空格替换为'%20'之后的长度
        int newLength = originalLength + numberOfBlank * 2;
        if (newLength > length) return;
        int indexOfOriginal = originalLength;
        int indexOfNew = newLength;
        while (indexOfOriginal >= 0 && indexOfNew > indexOfOriginal){
            if (string[indexOfOriginal] == ' '){
                string[indexOfNew --] = '0';
                string[indexOfNew --] = '2';
                string[indexOfNew --] = '%';
            }
            else {
                string[indexOfNew --] = string[indexOfOriginal];
            }
            --indexOfOriginal;
        }
    }

    public static void main(String[] args) {
        char[] string = new char[100];
        char[] test = "Hello World".toCharArray();
        System.arraycopy(test, 0, string, 0, test.length);
        ReplaceBlank(string, 100);
        System.out.println(new String(string).trim());
    }
}