Merge pull request #2562 from vamshi9/patch/100-dfs

Patch for 100 - dfs base case checks

Author: Ykhan799

javascript/0100-same-tree.js

@@ -1,29 +1,44 @@
 /**
- * https://leetcode.com/problems/same-tree/
- * TIme O(N) | Space O(H)
+ * Check if both nodes are null (end of a branch in both trees)
  * @param {TreeNode} p
  * @param {TreeNode} q
  * @return {boolean}
  */
-var isSameTree = function(p, q) {
-    const isBaseCase = !(p || q);
-    if (isBaseCase) return true;
+var isSameTree = function (p, q) {
+    // Check if both nodes are null (end of a branch in both trees)
+    const areBothNodesNull = p == null && q == null;
+    if (areBothNodesNull) return true;
 
-    const isBalanced = (p && q);
-    if (!isBalanced) return false;
+    // Check if only one node is null (mismatch in tree structure)
+    const isOnlyOneNodeNull = p == null || q == null;
+    if (isOnlyOneNodeNull) return false;
 
-    const isSame = p.val === q.val;
-    if (!isSame) return false;
+    // Check if node values are equal (mismatch in node values)
+    const doNodesHaveEqualValue = p.val == q.val;
+    if (!doNodesHaveEqualValue) return false;
 
+    // Recursively check left and right subtrees
     return dfs(p, q);
 };
 
+/**
+ * * https://leetcode.com/problems/same-tree/
+ * * Time complexity is O(N), where N is the total number of nodes in the tree.
+   * This is because in the worst-case scenario, we need to visit every node once.
+
+ * * Space complexity is O(H), where H is the height of the tree.
+   * This is because in the worst-case scenario (a skewed tree), the maximum
+   * amount of space is consumed by the recursive stack. 
+ * @param {*} p 
+ * @param {*} q 
+ * @returns 
+ */
 const dfs = (p, q) => {
     const left = isSameTree(p.left, q.left);
     const right = isSameTree(p.right, q.right);
 
     return left && right;
-}
+};
 
 /**
  * https://leetcode.com/problems/same-tree/
@@ -32,40 +47,41 @@ const dfs = (p, q) => {
  * @param {TreeNode} q
  * @return {boolean}
  */
-var isSameTree = function(p, q) {
+var isSameTree = function (p, q) {
     if (isSameNode(p, q)) return true;
 
-    return bfs([[ p, q ]]);
-}
+    return bfs([[p, q]]);
+};
 
 const bfs = (queue) => {
     while (queue.length) {
-        for (let i = (queue.length - 1); 0 <= i; i--) {
-            const [ p, q ] = queue.shift();
+        for (let i = queue.length - 1; 0 <= i; i--) {
+            const [p, q] = queue.shift();
 
             if (!isSame(p, q)) return false;
 
-            if (p.left) queue.push([ p.left, q.left ]);
-            if (p.right) queue.push([ p.right, q.right ]);
+            if (p.left) queue.push([p.left, q.left]);
+            if (p.right) queue.push([p.right, q.right]);
         }
     }
 
     return true;
-}
+};
 
 const isSameNode = (p, q) => {
     const isBaseCase = !(p || q);
     if (isBaseCase) return true;
 
-    const isBalanced = (p && q);
+    const isBalanced = p && q;
     if (!isBalanced) return false;
 
     const isSame = p.val === q.val;
     if (!isSame) return false;
 
     return true;
-}
+};
 
-const isSame = (p, q) => isSameNode(p, q)
-    && isSameNode(p.left, q.left)
-    && isSameNode(p.right, q.right);
+const isSame = (p, q) =>
+    isSameNode(p, q) &&
+    isSameNode(p.left, q.left) &&
+    isSameNode(p.right, q.right);