Leetcode394 string decoding

Title address LeetCode394. String decoding

https://leetcode-cn.com/problems/decode-string/

Title Description

 Given an encoded string , Returns the decoded string .
 The coding rule is : k[encoded_string], Represents the  encoded_string  Just repeat  k  Time . Be careful  k  Positive integer guaranteed .
 You can think that the input string is always valid ; There are no extra spaces in the input string , And the square brackets entered always meet the format requirements .
 Besides , You can assume that the raw data does not contain numbers , All numbers only indicate the number of repetitions  k , For example, there is no such thing as  3a  or  2[4]  The input of .

 Example  1：

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

 Example  2：

 Input ：s = "3[a2[c]]"
 Output ："accaccacc"

 Example  3：

 Input ：s = "2[abc]3[cd]ef"
 Output ："abcabccdcdcdef"

 Example  4：

 Input ：s = "abc3[cd]xyz"
 Output ："abccdcdcdxyz"

Ideas

Use the stack to save numbers and strings

Code

• Language support ：c++

c++ Code:

class Solution {
    
public:
    string decodeString(string s) {
    
        int len = s.size(), num = 0;
        stack<int> nums;
        stack<string> str;
        string res = "";
        for(int i=0; i<len; i++){
    
            if(s[i]>='0' && s[i]<='9'){
    
                num *= 10;
                num += (s[i]-'0');
            }
            else if(s[i]>='a' && s[i]<='z'){
    
                res += s[i];
            }
            else if(s[i]=='['){
    
                nums.push(num);
                str.push(res);
                res = "";
                num = 0;
            }
            else{
    
                int count = nums.top();
                nums.pop();
                while(count){
    
                    str.top() += res;
                    count--;
                }
                res = str.top();
                str.pop();
            }
        }
        return res;
    }
};