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394. Decode String
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].
Examples:
s = "3[a]2[bc]", return "aaabcbc".
s = "3[a2[c]]", return "accaccacc".
s = "2[abc]3[cd]ef", return "abcabccdcdcdef".思路分析
主要就是一个栈操作。不过，还需要注意一些细节。
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/**
* Runtime: 1 ms, faster than 64.03% of Java online submissions for Decode String.
* Memory Usage: 37.4 MB, less than 5.68% of Java online submissions for Decode String.
*
* @author D瓜哥 · https://www.diguage.com
* @since 2020-01-28 22:08
*/
public String decodeString(String s) {
if (Objects.isNull(s) || s.length() == 0) {
return "";
}
Deque<Integer> nums = new LinkedList<>();
Deque<String> strings = new LinkedList<>();
int num = 0;
StringBuilder result = new StringBuilder();
for (char c : s.toCharArray()) {
if (c == '[') {
nums.addLast(num);
strings.addLast(result.toString());
num = 0;
result = new StringBuilder();
} else if (c == ']') {
StringBuilder sb = new StringBuilder();
Integer n = nums.removeLast();
for (int i = 0; i < n; i++) {
sb.append(result);
}
result = new StringBuilder(strings.removeLast() + sb.toString());
} else if (Character.isDigit(c)) {
num = num * 10 + (c - '0');
} else if (Character.isLetter(c)) {
result.append(c);
}
}
return result.toString();
}
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/**
* @author D瓜哥 · https://www.diguage.com
* @since 2024-09-18 16:05:13
*/
int idx = 0;
public String decodeString(String s) {
StringBuilder sb = new StringBuilder();
while (idx < s.length()) {
char c = s.charAt(idx);
if ('0' <= c && c <= '9') {
sb.append(dfs(s));
} else {
sb.append(c);
idx++;
}
}
return sb.toString();
}
private String dfs(String s) {
int cnt = 0;
boolean isEnd = false;
StringBuilder sb = new StringBuilder();
while (idx < s.length()) {
char c = s.charAt(idx);
if ('0' <= c && c <= '9') {
if (isEnd) {
sb.append(dfs(s));
continue;
}
int num = c - '0';
if (cnt == 0) {
cnt = num;
} else {
cnt = 10 * cnt + num;
}
idx++;
} else if ('a' <= c && c <= 'z') {
sb.append(c);
idx++;
} else if (c == '[') {
isEnd = true;
idx++;
} else if (s.charAt(idx) == ']') {
idx++;
break;
}
}
StringBuilder result = new StringBuilder();
for (int j = 0; j < cnt; j++) {
result.append(sb);
}
return result.toString();
}