Leetcode 394 - Decode String

Note:

  • My first intuition was to use stack coz it gave us access to the last [ when we met a ].
  • When curr !== ], keep adding chars.
  • When curr === ], pop and record tops to tmp, and stop at [.
  • Then pop nums till top of stack is not a num string.
  • Repeat tmp n times as the num we’ve found, and push the result to stack.
  • Keep doing it, and return stack.join('').

Question:

Given an encoded string, return its decoded string.

The encoding rule is: k[encoded_string], where the encoded_string inside the square brackets is being repeated exactly k times. Note that k is guaranteed to be a positive integer.

You may assume that the input string is always valid; No extra white spaces, square brackets are well-formed, etc.

Furthermore, you may assume that the original data does not contain any digits and that digits are only for those repeat numbers, k. For example, there won’t be input like 3a or 2[4].

Example:

1
2
Input: s = "3[a]2[bc]"
Output: "aaabcbc"

Code:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
/**
* @param {string} s
* @return {string}
*/
var decodeString = function(s) {
let stack = [];
s = s.split('');
while (s.length > 0) {
const curr = s.shift();
if (curr === ']') {
let tmp = ''
while (stack.length && stack[stack.length - 1] !== '[') {
tmp = stack.pop() + tmp;
}
stack.pop();
let count = '';
while (!isNaN(stack[stack.length - 1])) {
count = stack.pop() + count;
}
tmp = tmp.repeat(count - 0);
stack.push(...tmp.split(''));
} else {
stack.push(curr);
}
}
return stack.join('');
};