Submission Week Ten

week10/generate_parentheses.cpp

@@ -0,0 +1,17 @@
+// Time complexity: O(2 ^ (2 * n)) 
+// Space complexity: O(2 ^ (2 * n))
+
+void generateBrackets(string currStr, int open, int close, vector<string> &bracket_list){
+    if(open == close && open == 0){
+        bracket_list.push_back(currStr);
+        return;
+    }
+    if(open > 0) generateBrackets(currStr + "(", open - 1, close, bracket_list);
+    if(open < close) generateBrackets(currStr + ")", open, close - 1, bracket_list);
+}
+
+vector<string> generateParentheses(int n){
+    vector<string> bracket_list;
+    generateBrackets("", n, n, bracket_list);
+    return bracket_list;
+}

week10/letter_combination_of_a_phone_number.cpp

@@ -0,0 +1,24 @@
+// Time complexity: O(N * 4 ^ N), N = Length of digits. 
+// Space complexity: O(N * 4 ^ N), N = Length of digits. 
+
+void genCombination(string currStr, int pos, string &digits, vector<string> &digitLetterList, vector<string> &combinationList){
+    if(pos == digits.size()){
+        combinationList.push_back(currStr);
+        return;
+    }
+    int digit = digits[pos] - '0';
+    for(auto letter: digitLetterList){
+        genCombination(currStr + letter, pos + 1, digits, digitLetterList, combinationList);
+    }
+}
+
+vector<string> letterCombinations(string digits){
+    if(digits.size() == 0) return {};
+    vector<string> combinationList;
+    vector<string> digitLetterList = {
+        "", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"
+    };
+    string currStr;
+    genCombination(currStr, 0, digits, digitLetterList, combinationList);
+    return combinationList;
+}

week10/subsets.cpp

@@ -0,0 +1,19 @@
+// Time complexity: O(2^N) , N = Number of elements in the array.
+// Space complexity: O(2^N), N = Number of elements in the array.
+
+void gen_subsets(int curr, vector<int> subset, vector<vector<int>> &subset_list, vector<int> &nums){
+    if(curr == nums.size()){
+        subset_list.push_back(subset);
+        return;
+    }
+    subset.push_back(nums[curr]);
+    gen_subsets(curr + 1, subset, subset_list, nums);
+    subset.pop_back();
+    gen_subsets(curr + 1, subset, subset_list, nums);
+}
+
+vector<vector<int>> subsets(vector<int> &nums){
+    vector<vector<int>> subset_list;
+    gen_subsets(0, {}, subset_list, nums);
+    return subset_list;
+}

week10/verify_preorder_sequence_in_binary_search_tree.cpp

@@ -0,0 +1,18 @@
+// Time complexity: O(N), N = Number of elements in an array.
+// Space complexity: O(N)
+//
+
+void verify_bst(vector<int> &preorder, int &curr_index,  int left, int right){
+    if(curr_index >= preorder.size()) return;
+    int value = preorder[curr_index];
+    if(value < left || value > right) return;
+    curr_index++;
+    verify_bst(preorder, curr_index, left, value - 1);
+    verify_bst(preorder, curr_index, value + 1, right);
+}
+
+bool verify_preorder(vector<int> &preorder){
+    int curr_index = 0;
+    verify_bst(preorder, curr_index, INT_MIN, INT_MAX);
+    return curr_index == preorder.size();
+}

week10/word_search.cpp

@@ -0,0 +1,31 @@
+// Time complexity: O(M * N * 3 ^ L), M = Width of the board, N = Height of the board, L = Word length.
+// Space complexity: O(L), L = Word length.
+
+int dx[4] = {0, 0, 1, -1};
+int dy[4] = {-1, 1, 0, 0};
+
+bool traverseBoard(vector<vector<char>> &board, string &word, int &m, int &n, int pos, int x, int y){
+    if(x < 0 || x >= m || y < 0 || y >= n || word[pos] != board[x][y]) return false;
+    if(pos == word.size() - 1) return true;
+    bool status = false;
+    char ch = board[x][y];
+    board[x][y] = '#';
+    for(int i = 0; i < 4; i++){
+        status |= traverseBoard(board, word, m, n, pos+1, x + dx[i], y + dy[i]);
+    }
+    board[x][y] = ch;
+    return status;
+}
+
+bool exist(vector<vector<char>> &board, string word){
+    if(word.size() == 0) return true;
+    if(board.size() == 0 || board[0].size() == 0) return false;
+    int m = board.size();
+    int n = board[0].size();
+    for(int i = 0; i < m; i++){
+        for(int j = 0; j < n; j++){
+            if(traverseBoard(board, word, m, n, 0, i, j)) return true;
+        }
+    }
+    return false;
+}