#### [剑指 Offer 05. 替换空格](https://leetcode-cn.com/problems/ti-huan-kong-ge-lcof/)

难度 简单

请实现一个函数，把字符串 `s` 中的每个空格替换成"%20"。

 

**示例 1：**

```
输入：s = "We are happy."
输出："We%20are%20happy."
```

 

**限制：**

```
0 <= s 的长度 <= 10000
```

#### 解法

```java
class Solution {
    public String replaceSpace(String s) {
        if (s == null || s.length() == 0) return s;
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < s.length(); i++) {
            if (s.charAt(i) == ' ') {
                sb.append("%20");
            } else {
                sb.append(s.charAt(i));
            }
        }
        return sb.toString();
    }
}
```

