🦁 Leetcode 🌱

Table of Contents

• 🦁 Leetcode 🌱
• Table of Contents
  • String to Int - Atoi
  • Is Palindrome
  • Regular Expression Matching
  • Container with most water
  • Integer to Roman
  • Validate Stack Sequences
  • Reverse Nodes in k-Group
  • Substring with Concatenation of All Words
  • Longest Valid Parentheses
  • Merge k Sorted Lists
  • Kids With the Greatest Number of Candies
  • Sudoku Solver
  • First Missing Positive
  • Trapping rain water
  • Wildcard Matching
  • N Queens
  • Valid number
  • Text Justification
  • 3 Sum
  • 3 Sum Closest
  • Letter combinations of a phone number
  • Jump Game II

String to Int - Atoi

int myAtoi(String s) {
  // Base condition
  if (s.length < 1) {
    return 0;
  }
  // MAX and MIN values for integers
  final int max = 2147483647;
  final int min = -2147483648;

  s = s.trim();

  // Counter
  int i = 0;
  // Flag to indicate if the number is negative
  bool isNegative = s.startsWith("-");
  // Flag to indicate if the number is positive
  bool isPositive = s.startsWith("+");

  if (isNegative) {
    i++;
  } else if (isPositive) {
    i++;
  }

  // This will store the converted number
  double number = 0;
  // Loop for each numeric character in the sing iff numeric characters are leading
  // characters in the sing
  while (i < s.length &&
      s[i].codeUnitAt(0) >= '0'.codeUnitAt(0) &&
      s[i].codeUnitAt(0) <= '9'.codeUnitAt(0)) {
    number = number * 10 + (s[i].codeUnitAt(0) - '0'.codeUnitAt(0));
    i++;
  }
  // Give back the sign to the converted number
  number = isNegative ? -number : number;
  if (number < min) {
    return min;
  }
  if (number > max) {
    return max;
  }
  return number.round();
}

Is Palindrome

bool isPalindrome(int x) {
  final String str = x.toString();
  return str == str.split('').reversed.join().toString();
}

Regular Expression Matching

bool isMatch(String s, String p) {
  final RegExp regExp = RegExp(p);
  return regExp.stringMatch(s) == s;
}

Container with most water

int maxArea(List<int> height) {
  int max = 0;

  int left = 0;
  int right = height.length - 1;

  while (left < right) {
    final res = min(height[left], height[right]) * (right - left);

    if (res > max) max = res;

    if (height[left] < height[right]) {
      left++;
    } else {
      right--;
    }
  }

  return max;
}

Integer to Roman

String intToRoman(int num) {
  // Define roman values and symbols
  final List<int> values = [1000, 500, 100, 50, 10, 5, 1];
  final List<String> romanSymbols = ['M', 'D', 'C', 'L', 'X', 'V', 'I'];

  List<String> result = [];

  for (int index = 0; index < values.length; index++) {
    final int romanValue = values[index];
    final int div = (num / romanValue).floor();

    if (div > 0) {
      num -= div * romanValue;
      result.addAll(
        List.generate(
          div,
          (i) => romanSymbols[index],
        ),
      );
    }

    if (index < values.length - 1) {
      for (int j = index + 1; j < values.length; j++) {
        if (values[j].toString()[0] == '1') {
          final int nextValue = values[j];
          final int combine2Symbols = romanValue - nextValue;
          if (num >= combine2Symbols && num % combine2Symbols <= nextValue) {
            num -= combine2Symbols;
            result.add(romanSymbols[j]);
            result.add(romanSymbols[index]);
          }
        }
      }
    }
  }

  return result.join();
}

Validate Stack Sequences

bool validateStackSequences(List<int> pushed, List<int> popped) {
  List<int> current = [];
  int indexPush = 0;
  int indexPop = 0;

  while (indexPush < pushed.length - 1 || indexPop < popped.length - 1) {
    if (current.contains(popped[indexPop])) {
      if (current.last == popped[indexPop]) {
        current.removeLast();
        indexPop++;
      } else {
        return false;
      }
    } else {
      current.add(pushed[indexPush]);
      indexPush++;
    }
  }

  return true;
}

Reverse Nodes in k-Group

ListNode? reverseKGroup(ListNode? head, int k) {
  final List<int> values = mergeValue(head, []);
  final List<List<int>> chunks = [];

  for (int i = 0; i < values.length; i += k) {
    var end = (i + k < values.length) ? i + k : values.length;
    chunks.add(values.sublist(i, end));
  }

  final List<int> result = [];

  chunks.forEach((e) {
    if (e.length == k)
      result.addAll(e.reversed);
    else
      result.addAll(e);
  });

  return linkedNodes(result);
}

List<int> mergeValue(ListNode? head, List<int> result) {
  if (head == null) return result;

  return mergeValue(head.next, [...result, head.val]);
}

ListNode linkedNodes(List<int> values) {
  List<ListNode> nodes = values.map((e) => ListNode(e)).toList();

  for (int i = 0; i < nodes.length - 1; i++) {
    nodes[i].next = nodes[i + 1];
  }

  return nodes.first;
}

Substring with Concatenation of All Words

List<int> findSubstring(String s, List<String> words) {
  if (words.isEmpty || s.isEmpty || words.first.isEmpty) return [];

  final List<int> startIndexs = [];

  final int k = words.first.length;
  final int lengthOfMatchWords = words.length * k;
  final listCloned = words.map((e) => e).toList();

  listCloned.sort();

  if (s.length < lengthOfMatchWords) return [];

  for (final word in words.toSet().toList()) {
    final RegExp regExp = RegExp('(?=($word))');
    final Iterable<Match> matches = regExp.allMatches(s);

    if (matches.isEmpty) break;

    for (final match in matches) {
      if (match.start + lengthOfMatchWords <= s.length) {
        final String subString = s.substring(
          match.start,
          match.start + lengthOfMatchWords,
        );

        final List<String> chunks = [];

        for (int i = 0; i < subString.length; i += k) {
          var end = (i + k < subString.length) ? i + k : subString.length;
          chunks.add(subString.substring(i, end));
        }

        chunks.sort();

        // Check match with requiments
        if (chunks.join() == listCloned.join() &&
            !startIndexs.contains(match.start)) {
          startIndexs.add(match.start);
        }
      }
    }
  }

  startIndexs.sort();

  return startIndexs;
}

Longest Valid Parentheses

int longestValidParentheses(String s) {
  if (s.isEmpty) return 0;

  int longest = 0;
  final List<int> stack = [-1];

  for (int i = 0; i < s.length; i++) {
    // Open
    if (s[i] == '(') {
      stack.add(i);
    } else {
      if (stack.isNotEmpty) stack.removeLast();

      if (stack.isNotEmpty) {
        longest = max(longest, i - stack.last);
      } else {
        stack.add(i);
      }
    }
  }

  return longest;
}

Merge k Sorted Lists

ListNode? mergeKLists(List<ListNode?> lists) {
  List<int> merge = [];

  for (final list in lists) {
    merge.addAll(mergeValue(list, []));
  }

  merge.sort();

  return linkedNodes(merge);
}

// Utils
List<int> mergeValue(ListNode? head, List<int> result) {
  if (head == null) return result;

  return mergeValue(head.next, [...result, head.val]);
}

ListNode? linkedNodes(List<int> values) {
  if (values.isEmpty) return null;

  List<ListNode> nodes = values.map((e) => ListNode(e)).toList();

  for (int i = 0; i < nodes.length - 1; i++) {
    nodes[i].next = nodes[i + 1];
  }

  return nodes.first;
}

Kids With the Greatest Number of Candies

List<bool> kidsWithCandies(List<int> candies, int extraCandies) {
  final List<int> clone = candies.map((e) => e).toList();
  clone.sort((a, b) => b - a);
  int greatest = clone.first;

  final List<bool> result = candies.map((e) {
    return e + extraCandies >= greatest;
  }).toList();

  return result;
}

Sudoku Solver

void solveSudoku(List<List<String>> board) {
  _solver(board);
}

bool _solver(List<List<String>> board) {
  for (int i = 0; i < board.length; i++) {
    for (int j = 0; j < board.length; j++) {
      if (board[i][j] == '.') {
        for (int k = 1; k <= 9; k++) {
          if (_isValid(board, i, j, k)) {
            board[i][j] = '$k';

            if (_solver(board)) return true;
          }
        }

        board[i][j] = '.';
        return false;
      }
    }
  }

  print(board);

  return true;
}

bool _isValid(List<List<String>> board, int row, int col, int k) {
  for (int i = 0; i < 9; i++) {
    if (board[row][i] == '$k' || board[i][col] == '$k') {
      return false;
    }
  }

  final m = (col / 3).floor() * 3;
  final n = (row / 3).floor() * 3;

  for (int i = 0; i < 3; i++) {
    for (int j = 0; j < 3; j++) {
      if (board[n + i][m + j] == '$k') {
        return false;
      }
    }
  }

  return true;
}

First Missing Positive

int firstMissingPositive(List<int> nums) {
  nums = nums.where((e) => e > 0).toSet().toList();
  nums.sort();

  if (nums.isEmpty || nums.first != 1) return 1;

  for (int index = 1; index < nums.length; index++) {
    if (nums[index] - nums[index - 1] != 1) {
      return nums[index - 1] + 1;
    }
  }

  return nums.last + 1;
}

Trapping rain water

int trap(List<int> height) {
  if (height.length < 2) return 0;

  List<int> left = List.generate(height.length, (index) => 0);

  List<int> right = List.generate(height.length, (index) => 0);

  int result = 0;

  left.first = height.first;
  for (int i = 1; i < height.length; i++) {
    left[i] = max(left[i - 1], height[i]);
  }

  right.last = height.last;
  for (int i = height.length - 2; i >= 0; i--) {
    right[i] = max(right[i + 1], height[i]);
  }

  for (int i = 0; i < height.length; i++) {
    result += min(left[i], right[i]) - height[i];
  }

  return result;
}

Wildcard Matching

bool isMatch(String s, String p) {
  if (p.replaceAll("*", "").length > s.length) return false;

  List<bool> flags = List.generate(s.length + 1, (index) => false);
  flags.first = true;
  for (int i = 1; i < s.length; ++i) {
    flags[i] = false;
  }

  for (int i = 1; i <= p.length; ++i) {
    String char = p[i - 1];
    if (char == '*') {
      for (int j = 1; j <= s.length; ++j) {
        flags[j] = flags[j - 1] || flags[j];
      }
    } else {
      for (int j = s.length; j >= 1; --j) {
        flags[j] = flags[j - 1] && (char == '?' || char == s[j - 1]);
      }
    }
    flags[0] = flags[0] && char == '*';
  }
  return flags[s.length];
}

N Queens

List<List<String>> solveNQueens(int n) {
  final List<List<String>> result = [];
  final List<List<String>> board = List.generate(
    n,
    (index) => List.generate(n, (index) => "."),
  );

  place(0, 0, 0, 0, board, result);

  return result;
}

void place(
  int i,
  int vert,
  int ldiag,
  int rdiag,
  List<List<String>> board,
  List<List<String>> result,
) {
  if (i == board.length) {
    List<String> res = [];
    for (final row in board) res.add(row.join());
    result.add(res);
    return;
  }

  for (int j = 0; j < board.length; j++) {
    int verticalMask = 1 << j,
        leftMask = 1 << (i + j),
        rightMask = 1 << (board.length - i - 1 + j);
    if ((vert & verticalMask) + (ldiag & leftMask) + (rdiag & rightMask) > 0) continue;
    board[i][j] = 'Q';
    place(i + 1, vert | verticalMask, ldiag | leftMask, rdiag | rightMask, board, result);
    board[i][j] = '.';
  }
}

Valid number

bool isNumber(String s) {
  if (s == "Infinity" || s == "-Infinity" || s == "+Infinity") return false;

  return num.tryParse(s) != null;
}

Text Justification

List<String> fullJustify(List<String> words, int maxWidth) {
  final List<String> result = [];
  String temp = '';

  for (int index = 0; index < words.length; index++) {
    final String word = words[index];

    if (temp.length + word.length + (temp.isEmpty ? 0 : 1) <= maxWidth) {
      temp += '${temp.isEmpty ? '' : ' '}$word';
    } else {
      if (temp.trim().isNotEmpty) {
        result.add(temp.trim());
      }
      temp = word;
    }

    if (index == words.length - 1 && temp.isNotEmpty) {
      result.add(temp.trim());
    }
  }

  return fillSpace(result, maxWidth);
}

List<String> fillSpace(List<String> words, int maxWidth) {
  for (int i = 0; i < words.length; i++) {
    final String word = words[i];
    if (word.length < maxWidth) {
      final List<String> splits = word.split(' ');
      if (splits.length < 2 || i == words.length - 1) {
        words[i] =
            word + List.generate(maxWidth - word.length, (index) => ' ').join();
      } else {
        int leftSpace = maxWidth - word.length + splits.length - 1;
        String temp = '';

        for (int j = 0; j < splits.length; j++) {
          final double div = leftSpace / (splits.length - j);
          int avgSpace = div.round();
          if (leftSpace / avgSpace > 0) {
            avgSpace = div.ceil();
          }

          if (j == 0) {
            temp += splits[j];
          } else if (leftSpace > 0) {
            final int cal = leftSpace < avgSpace ? leftSpace : avgSpace;
            temp += '${List.generate(cal, (index) => ' ').join()}${splits[j]}';
            leftSpace -= cal;
          }
        }

        words[i] = temp;
      }
    }
  }

  return words;
}

3 Sum

List<List<int>> threeSum(List<int> nums) {
  nums.sort();

  final List<List<int>> result = [];

  for (int i = 0; i < nums.length - 2; i++) {
    if (i > 0 && nums[i] == nums[i - 1]) continue;

    int left = i + 1;
    int right = nums.length - 1;

    while (left < right) {
      final int sum = nums[i] + nums[left] + nums[right];

      if (sum == 0) {
        result.add([nums[i], nums[left], nums[right]]);

        // remove duplicate
        while (left < nums.length - 1 && nums[left] == nums[left + 1]) left++;
        while (right > 0 && nums[right] == nums[right - 1]) right--;
        left++;
        right--;
      } else if (sum < 0) {
        left++;
      } else {
        right--;
      }
    }
  }

  return result;
}

3 Sum Closest

int threeSumClosest(List<int> nums, int target) {
  int result = -1;
  int diff = -1;

  for (int i = 0; i < nums.length - 2; i++) {
    int left = i + 1;
    int right = nums.length - 1;

    while (left < right) {
      final int sum = nums[i] + nums[left] + nums[right];

      if (diff < 0 || (sum - target).abs() < diff) {
        diff = (sum - target).abs();
        result = sum;
      }

      if (diff == 0) {
        return result;
      }

      if (right == left + 1) {
        left++;
        right = nums.length - 1;
      } else {
        right--;
      }
    }
  }

  return result;
}

Letter combinations of a phone number

const Map<int, List<String>> chars = {
  2: ['a', 'b', 'c'],
  3: ['d', 'e', 'f'],
  4: ['g', 'h', 'i'],
  5: ['k', 'j', 'l'],
  6: ['m', 'n', 'o'],
  7: ['p', 'q', 'r', 's'],
  8: ['t', 'u', 'v'],
  9: ['w', 'x', 'y', 'z'],
};

List<String> letterCombinations(String digits) {
  if (digits.isEmpty) return [];

  final List<String> result = [];

  lookupChar(0, "", digits.length, digits, result);

  return result;
}

void lookupChar(
  int index,
  String res,
  int length,
  String digits,
  List<String> result,
) {
  if (index == digits.length)
    result.add(res);
  else {
    final List<String> letters = chars[int.parse(digits[index])]!;
    for (int i = 0; i < letters.length; i++) {
      lookupChar(index + 1, res + letters[i], length, digits, result);
    }
  }
}

Jump Game II

int jump(List<int> nums) {
  if (nums.isEmpty) return 0;

  int result = 0;
  int maxNumber = 0;
  int cur = 0;

  for (var i = 0; i < nums.length - 1; i++) {
    maxNumber = max(maxNumber, i + nums[i]);
    if (i == cur) {
      result++;
      cur = maxNumber;
    }
  }

  return result;
}