# 394. Decode String

Given an encoded string, return it’s 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]`.

Examples:

``````s = "3[a]2[bc]", return "aaabcbc".
s = "3[a2[c]]", return "accaccacc".
s = "2[abc]3[cd]ef", return "abcabccdcdcdef".
``````

``````class Solution {
public:
string decodeString(string s) {
int i = 0;
return decode(s, i);
}
string decode(string s, int& i) {
string res = "";
int n = s.size();
while (i < n && s[i] != ']') {
if (s[i] < '0' || s[i] > '9') {
res += s[i++];
} else {
int cnt = 0;
while (s[i] >= '0' && s[i] <= '9') {
cnt = cnt * 10 + s[i++] - '0';
}
++i;
string t = decode(s, i);
++i;
while (cnt-- > 0) {
res += t;
}
}
}
return res;
}
};
``````

``````class Solution {
public:
string decodeString(string s) {
string t = "";
stack<int> s_num;
stack<string> s_str;
int cnt = 0;
for (int i = 0; i < s.size(); ++i) {
if (s[i] >= '0' && s[i] <= '9') {
cnt = 10 * cnt + s[i] - '0';
} else if (s[i] == '[') {
s_num.push(cnt);
s_str.push(t);
cnt = 0; t.clear();
} else if (s[i] == ']') {
int k = s_num.top(); s_num.pop();
for (int j = 0; j < k; ++j) s_str.top() += t;
t = s_str.top(); s_str.pop();
} else {
t += s[i];
}
}
return s_str.empty() ? t : s_str.top();
}
};
``````

Encode String with Shortest Length

Number of Atoms

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

https://leetcode.com/problems/decode-string/discuss/87728/share-my-c-solution

https://leetcode.com/problems/decode-string/discuss/87543/0ms-simple-C%2B%2B-solution

LeetCode All in One 题目讲解汇总(持续更新中…)

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