剑指offer:面试题4、替换空格

题目描述

请实现一个函数，将一个字符串中的每个空格替换成“%20”。例如，当字符串为We Are Happy.则经过替换之后的字符串为We%20Are%20Happy。

代码示例

public class Offer4 {
    public static void main(String[] args) {
        Offer4 testObj = new Offer4();
        StringBuffer sb = new StringBuffer("hello world");
        System.out.println(testObj.replaceSpace(sb));
    }

    public String replaceSpace(StringBuffer str) {
        int beforeLength = str.length() - 1;
        for (int i = 0; i <= beforeLength; i++) {
            if (str.charAt(i) == ' ') {
                str.append("  ");//添加两个空格
            }
        }
        int afterLength = str.length() - 1;
        while (afterLength > beforeLength && beforeLength >= 0) {
            char ch = str.charAt(beforeLength--);
            if (ch == ' ') {
                str.setCharAt(afterLength--, '0');
                str.setCharAt(afterLength--, '2');
                str.setCharAt(afterLength--, '%');
            } else {
                str.setCharAt(afterLength--, ch);
            }
        }
        return str.toString();
    }
}