Formatted question description: https://leetcode.ca/all/1209.html
1209. Remove All Adjacent Duplicates in String II (Medium)
Given a string s
, a k duplicate removal consists of choosing k
adjacent and equal letters from s
and removing them causing the left and the right side of the deleted substring to concatenate together.
We repeatedly make k
duplicate removals on s
until we no longer can.
Return the final string after all such duplicate removals have been made.
It is guaranteed that the answer is unique.
Example 1:
Input: s = "abcd", k = 2 Output: "abcd" Explanation: There's nothing to delete.
Example 2:
Input: s = "deeedbbcccbdaa", k = 3 Output: "aa" Explanation: First delete "eee" and "ccc", get "ddbbbdaa" Then delete "bbb", get "dddaa" Finally delete "ddd", get "aa"
Example 3:
Input: s = "pbbcggttciiippooaais", k = 2 Output: "ps"
Constraints:
1 <= s.length <= 10^5
2 <= k <= 10^4
s
only contains lower case English letters.
Related Topics:
Stack
Similar Questions:
Solution 1. Stack
// OJ: https://leetcode.com/problems/remove-all-adjacent-duplicates-in-string-ii/
// Time: O(N)
// Space: O(N)
class Solution {
public:
string removeDuplicates(string s, int k) {
vector<pair<char, int>> st;
for (char c : s) {
if (st.empty() || st.back().first != c) st.emplace_back(c, 1);
else if (++st.back().second == k) st.pop_back();
}
string ans;
for (int i = 0; i < st.size(); ++i) {
for (int j = 0; j < st[i].second; ++j) ans += st[i].first;
}
return ans;
}
};
Java
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class Solution { public String removeDuplicates(String s, int k) { StringBuffer sb = new StringBuffer(); List<Integer> duplicatesCounts = new ArrayList<Integer>(); int length = s.length(); for (int i = 0; i < length; i++) { int curLength = sb.length(); char c = s.charAt(i); int curCount = 1; if (curLength > 0 && c == sb.charAt(curLength - 1)) curCount = duplicatesCounts.get(curLength - 1) + 1; if (curCount == k) { int startIndex = curLength - k + 1; sb.delete(startIndex, curLength); for (int j = curLength - 1; j >= startIndex; j--) duplicatesCounts.remove(j); } else { sb.append(c); duplicatesCounts.add(curCount); } } return sb.toString(); } }
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// OJ: https://leetcode.com/problems/remove-all-adjacent-duplicates-in-string-ii/ // Time: O(N) // Space: O(N) class Solution { public: string removeDuplicates(string s, int k) { vector<pair<char, int>> st; for (char c : s) { if (st.empty() || st.back().first != c) st.emplace_back(c, 1); else if (++st.back().second == k) st.pop_back(); } string ans; for (auto &[c, cnt] : st) { while (cnt--) ans += c; } return ans; } };
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# 1209. Remove All Adjacent Duplicates in String II # https://leetcode.com/problems/remove-all-adjacent-duplicates-in-string-ii/ class Solution: def removeDuplicates(self, s: str, k: int) -> str: stack = [] for c in s: if stack and stack[-1][0] == c: ch, cnt = stack.pop() stack.append((ch, cnt + 1)) else: stack.append((c, 1)) if stack and stack[-1][1] == k: stack.pop() return "".join(ch * cnt for ch, cnt in stack)