【问题描述】[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

【解答思路】

1. 复制大法

时间复杂度：O(N) 空间复杂度：O(N)

class Solution {public String replaceSpace(String s) {int length = s.length();char[] array = new char[length * 3];int size = 0;for (int i = 0; i < length; i++) {char c = s.charAt(i);if (c == ' ') {array[size++] = '%';array[size++] = '2';array[size++] = '0';} else {array[size++] = c;}}String newStr = new String(array, 0, size);return newStr;}
}

2. StringBuilder/Buffer

时间复杂度：O(N) 空间复杂度：O(N)

class Solution {public String replaceSpace(String s) {StringBuilder res = new StringBuilder();for(Character c : s.toCharArray()){if(c == ' ') res.append("%20");else res.append(c);}return res.toString();}
}

【总结】

1.Java StringBuffer 和 StringBuilder 类

2.处理字符串 逐个比较

2.1转换字符数组（推荐）char[]ch=s.toCharArray();
2.2 使用charAt() char c = s.charAt()

转载链接：https://leetcode-cn.com/problems/ti-huan-kong-ge-lcof/solution/mian-shi-ti-05-ti-huan-kong-ge-ji-jian-qing-xi-tu-/
来源：力扣（LeetCode）
参考链接：https://www.runoob.com/java/java-stringbuffer.html