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Problem solution · C++

Longest Substring of One Repeating Character

Longest Substring of One Repeating Character: a C++ solution using segment tree or range structure. Learn the idea, check the complexity, and read the full code, with credit to walkccc LeetCode Solutions.

Technique
Segment tree or range structure
Source
walkccc LeetCode Solutions
Length
129 lines
Start with the idea.

Try the problem first. If you get stuck, read the approach below, then write your own solution. The full code is at the bottom.

Approach

Segment tree or range structure

For Longest Substring of One Repeating Character, the implementation stores interval information in a range-query data structure so updates and queries avoid rescanning the full input.

  1. Choose the aggregate stored for each interval or prefix.
  2. Build or initialize the structure from the input.
  3. Apply updates and combine the affected nodes to answer each query.

Code notes

  • 129 lines of C++ from the credited upstream file 2213.cpp.
  • The implementation visibly relies on sequence storage.
  • 1 loop block detected.

Complexity

Count the build once, then multiply the logarithmic update or query path by the number of operations.

Check the problem constraints before deciding whether this complexity will pass.

Source

Code and credit

This code comes from walkccc LeetCode Solutions by P.-Y. Chen (walkccc) and is used under the MIT licence.

Open problem ↗Original source ↗
Full codeLongest Substring of One Repeating Character · C++C++
Use this to learn the idea, then write your own version.
struct SegmentTreeNode {  int lo;  int hi;  char maxLetter;  char prefixLetter;  char suffixLetter;  int maxLength;  int prefixLength;  int suffixLength;  SegmentTreeNode* left;  SegmentTreeNode* right;  SegmentTreeNode(int lo, int hi, char maxLetter, char prefixLetter,                  char suffixLetter, int maxLength, int prefixLength,                  int suffixLength, SegmentTreeNode* left = nullptr,                  SegmentTreeNode* right = nullptr)      : lo(lo),        hi(hi),        maxLetter(maxLetter),        prefixLetter(prefixLetter),        suffixLetter(suffixLetter),        maxLength(maxLength),        prefixLength(prefixLength),        suffixLength(suffixLength),        left(left),        right(right) {}  ~SegmentTreeNode() {    delete left;    delete right;    left = nullptr;    right = nullptr;  }}; class SegmentTree { public:  explicit SegmentTree(const string& s) : root(build(s, 0, s.length() - 1)) {}  ~SegmentTree() {    delete root;  }   void update(int i, char val) {    root = update(root, i, val);  }   int getMaxLength() {    return root->maxLength;  }  private:  SegmentTreeNode* root;   SegmentTreeNode* build(const string& s, int lo, int hi) const {    if (lo == hi)      return new SegmentTreeNode(lo, hi, s[lo], s[lo], s[lo], 1, 1, 1);    const int mid = (lo + hi) / 2;    SegmentTreeNode* left = build(s, lo, mid);    SegmentTreeNode* right = build(s, mid + 1, hi);    return merge(left, right);  }   SegmentTreeNode* update(SegmentTreeNode* root, int i, char c) {    if (root->lo == i && root->hi == i) {      root->maxLetter = c;      root->prefixLetter = c;      root->suffixLetter = c;      return root;    }    const int mid = (root->lo + root->hi) / 2;    if (i <= mid) {      SegmentTreeNode* updatedLeft = update(root->left, i, c);      return root = merge(updatedLeft, root->right);    } else {      SegmentTreeNode* updatedRight = update(root->right, i, c);      return root = merge(root->left, updatedRight);    }  }   SegmentTreeNode* merge(SegmentTreeNode* left, SegmentTreeNode* right) const {    // Get `maxLetter` and `maxLength`.    char maxLetter = ' ';    int maxLength = 0;    if (left->maxLength > right->maxLength) {      maxLetter = left->maxLetter;      maxLength = left->maxLength;    } else {      maxLetter = right->maxLetter;      maxLength = right->maxLength;    }    if (left->suffixLetter == right->prefixLetter &&        left->suffixLength + right->prefixLength > maxLength) {      maxLetter = left->suffixLetter;      maxLength = left->suffixLength + right->prefixLength;    }     // Get `prefixLetter` and `prefixLength`.    char prefixLetter = left->prefixLetter;    int prefixLength = left->prefixLength;    if (left->lo + prefixLength == right->lo &&        left->prefixLetter == right->prefixLetter)      prefixLength += right->prefixLength;     // Get `suffixLetter` and `suffixLength`.    char suffixLetter = right->suffixLetter;    int suffixLength = right->suffixLength;    if (right->hi - suffixLength == left->hi &&        right->suffixLetter == left->suffixLetter)      suffixLength += left->suffixLength;    return new SegmentTreeNode(left->lo, right->hi, maxLetter, prefixLetter,                               suffixLetter, maxLength, prefixLength,                               suffixLength, left, right);  }}; class Solution { public:  vector<int> longestRepeating(string s, string queryLetteracters,                               vector<int>& queryIndices) {    vector<int> ans;    SegmentTree tree(s);     for (int i = 0; i < queryIndices.size(); ++i) {      tree.update(queryIndices[i], queryLetteracters[i]);      ans.push_back(tree.getMaxLength());    }     return ans;  }};

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