Add week 9 solutions: designAddAndSearchWordsDatatStructure, numberOfIslands

Author: yolophg

design-add-and-search-words-data-structure/yoloophg.js

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+// AddWord Method : Time Complexity: O(L)/Space Complexity: O(L)
+// Search Method : Time Complexity: O(M)/Space Complexity: O(1)
+// SearchInNode Method : Time Complexity: O(M)/Space Complexity: O(1)
+
+var WordDictionary = function () {
+  this.root = {};
+};
+
+WordDictionary.prototype.addWord = function (word) {
+  // start from the root node
+  let node = this.root;
+  for (let char of word) {
+    if (!node[char]) {
+      // if the character does not exist, create a new node
+      node[char] = {};
+    }
+    // move to the next node
+    node = node[char];
+  }
+  // mark the end of the word
+  node.isEndOfWord = true;
+};
+
+WordDictionary.prototype.search = function (word) {
+  // start searching from the root
+  return this.searchInNode(word, 0, this.root);
+};
+
+WordDictionary.prototype.searchInNode = function (word, index, node) {
+  if (index === word.length) {
+    // if all characters are checked
+    return node.isEndOfWord === true;
+  }
+
+  const char = word[index];
+  if (char === ".") {
+    //iIf the character is '.', check all possible nodes at this part
+    for (let key in node) {
+      if (
+        key !== "isEndOfWord" &&
+        this.searchInNode(word, index + 1, node[key])
+      ) {
+        // if any path matches, return true
+        return true;
+      }
+    }
+    // no path matched
+    return false;
+  } else if (node[char]) {
+    // if the character exists in the trie
+    return this.searchInNode(word, index + 1, node[char]);
+  } else {
+    // character path does not exist
+    return false;
+  }
+};

number-of-islands/yolophg.js

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+// Time Complexity: O(m * n)
+// Space Complexity: O(m * n)
+
+var numIslands = function (grid) {
+  const m = grid.length;
+  const n = grid[0].length;
+  let numIslands = 0;
+
+  // directions arrays for moving up, down, left, and right
+  const directions = [
+    [-1, 0],
+    [1, 0],
+    [0, -1],
+    [0, 1],
+  ];
+
+  // BFS function
+  function bfs(row, col) {
+    const queue = [[row, col]];
+    // mark as visited
+    grid[row][col] = "0";
+
+    while (queue.length > 0) {
+      const [r, c] = queue.shift();
+
+      for (const [dr, dc] of directions) {
+        const nr = r + dr;
+        const nc = c + dc;
+
+        if (nr >= 0 && nr < m && nc >= 0 && nc < n && grid[nr][nc] === "1") {
+          // mark as visited
+          grid[nr][nc] = "0";
+          queue.push([nr, nc]);
+        }
+      }
+    }
+  }
+
+  // iterate through each cell in the grid
+  for (let i = 0; i < m; i++) {
+    for (let j = 0; j < n; j++) {
+      if (grid[i][j] === "1") {
+        numIslands++;
+        // start BFS to mark all connected land cells
+        bfs(i, j);
+      }
+    }
+  }
+
+  return numIslands;
+};