leetcode271- Encode and Decode Strings- medium
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Design an algorithm to encode a list of strings to a string. The encoded string is then sent over the network and is decoded back to the original list of strings.
Machine 1 (sender) has the function:
string encode(vector<string> strs) { // ... your code return encoded_string; }
Machine 2 (receiver) has the function:
vector<string> decode(string s) { //... your code return strs; }
So Machine 1 does:
string encoded_string = encode(strs);
and Machine 2 does:
vector<string> strs2 = decode(encoded_string);
strs2
in Machine 2 should be the same as strs
in Machine 1.
Implement the encode
and decode
methods.
Note:
- The string may contain any possible characters out of 256 valid ascii characters. Your algorithm should be generalized enough to work on any possible characters.
- Do not use class member/global/static variables to store states. Your encode and decode algorithms should be stateless.
- Do not rely on any library method such as
eval
or serialize methods. You should implement your own encode/decode algorithm.
本题难度不在对字符加密,而在怎么把各个字符串分开。本来字符已经占用了任意可用的256种了,所以你不能简单地选一个分隔符然后用split。
最后用的方法是,加密时用 长度+‘#‘+真正字符串的形式去加(实践真的可行,哪怕实际有分隔符的字符,因为你说明了长度了你把它取出来后下一个使用indexOf就不会影响了。而且第一个分隔符肯定来自于真正的分隔符,所以递推下去就都不会有问题了)。
解密时每次 1.indexOf(‘#‘, idx),从指针所指的位置开始找第一个分隔符。2.上个指针到当前分割点语意理解后就是字符串长度。3.后面取出字符串即可。
实现:
public class Codec { // Encodes a list of strings to a single string. public String encode(List<String> strs) { StringBuilder sb = new StringBuilder(); for (int i = 0; i < strs.size(); i++) { sb.append(strs.get(i).length()); sb.append(‘#‘); sb.append(strs.get(i)); } return sb.toString(); } // Decodes a single string to a list of strings. public List<String> decode(String s) { List<String> result = new ArrayList<>(); int idx = 0; while (idx < s.length()) { int cut = s.indexOf(‘#‘, idx); int length = Integer.parseInt(s.substring(idx, cut)); result.add(s.substring(cut + 1, cut + 1 + length)); idx = cut + length + 1; } return result; } } // Your Codec object will be instantiated and called as such: // Codec codec = new Codec(); // codec.decode(codec.encode(strs));
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