271. Encode and Decode Strings
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.
Rust Solution
struct Codec;
use std::iter::FromIterator;
impl Codec {
fn new() -> Self {
Codec {}
}
fn encode(&self, strs: Vec<String>) -> String {
let n = strs.len();
let mut res: String = "".to_string();
let v = Self::encode_usize(n);
res.push_str(&v);
for s in strs {
let n = s.len();
let v = Self::encode_usize(n);
res.push_str(&v);
res.push_str(&s);
}
res
}
fn decode(&self, s: String) -> Vec<String> {
let mut res = vec![];
let v: Vec<char> = s.chars().collect();
let n = Self::decode_usize(&v[0..4]);
let mut index = 4;
for _ in 0..n {
let m = Self::decode_usize(&v[index..index + 4]);
index += 4;
let ss = String::from_iter(v[index..index + m].iter());
index += m;
res.push(ss);
}
res
}
fn encode_usize(x: usize) -> String {
let x = x as u32;
vec![
(x >> 24 & 0xff) as u8 as char,
(x >> 16 & 0xff) as u8 as char,
(x >> 8 & 0xff) as u8 as char,
(x & 0xff) as u8 as char,
]
.into_iter()
.collect()
}
fn decode_usize(v: &[char]) -> usize {
((v[0] as u32) << 24 | (v[1] as u32) << 16 | (v[2] as u32) << 8 | (v[3] as u32)) as usize
}
}
#[test]
fn test() {
let obj = Codec::new();
let strs = vec_string!("123", "321");
let encoded = obj.encode(strs);
let decoded = obj.decode(encoded);
let res = vec_string!("123", "321");
assert_eq!(decoded, res);
}
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