From 27feb10c27ca6afec21035127e798a55662ddac0 Mon Sep 17 00:00:00 2001
From: Manish <manish@radii.dev>
Date: Fri, 1 Sep 2023 18:17:58 +1000
Subject: [PATCH] Data Structures: BST DFS using iteration rather than
 recursion

---
 Data Structures/bstDFS.js | 72 +++++++++++++++++++++++++++++----------
 1 file changed, 54 insertions(+), 18 deletions(-)

diff --git a/Data Structures/bstDFS.js b/Data Structures/bstDFS.js
index 903eb8e..6295a59 100644
--- a/Data Structures/bstDFS.js	
+++ b/Data Structures/bstDFS.js	
@@ -14,12 +14,24 @@ function BinarySearchTree() {
       return null;
     }
     const values = [];
-    const traverse = (node) => {
-      if (node.left !== null) traverse(node.left);
-      values.push(node.value);
-      if (node.right !== null) traverse(node.right);
-    };
-    traverse(this.root);
+    const stack = [{ node: this.root, stage: "left" }];
+    while (stack.length) {
+      const { node, stage } = stack[stack.length - 1];
+      if (stage === "left") {
+        stack[stack.length - 1].stage = "node";
+        if (node.left !== null) {
+          stack.push({ node: node.left, stage: "left" });
+        }
+      } else if (stage === "node") {
+        stack[stack.length - 1].stage = "right";
+        values.push(node.value);
+      } else if (stage === "right") {
+        stack.pop();
+        if (node.right !== null) {
+          stack.push({ node: node.right, stage: "left" });
+        }
+      }
+    }
     return values;
   };
 
@@ -28,12 +40,24 @@ function BinarySearchTree() {
       return null;
     }
     const values = [];
-    const traverse = (node) => {
-      values.push(node.value);
-      if (node.left !== null) traverse(node.left);
-      if (node.right !== null) traverse(node.right);
-    };
-    traverse(this.root);
+    const stack = [{ node: this.root, stage: "node" }];
+    while (stack.length) {
+      const { node, stage } = stack[stack.length - 1];
+      if (stage === "node") {
+        stack[stack.length - 1].stage = "left";
+        values.push(node.value);
+      } else if (stage === "left") {
+        stack[stack.length - 1].stage = "right";
+        if (node.left !== null) {
+          stack.push({ node: node.left, stage: "node" });
+        }
+      } else if (stage === "right") {
+        stack.pop();
+        if (node.right !== null) {
+          stack.push({ node: node.right, stage: "node" });
+        }
+      }
+    }
     return values;
   };
 
@@ -42,12 +66,24 @@ function BinarySearchTree() {
       return null;
     }
     const values = [];
-    const traverse = (node) => {
-      if (node.left !== null) traverse(node.left);
-      if (node.right !== null) traverse(node.right);
-      values.push(node.value);
-    };
-    traverse(this.root);
+    const stack = [{ node: this.root, stage: "left" }];
+    while (stack.length) {
+      const { node, stage } = stack[stack.length - 1];
+      if (stage === "left") {
+        stack[stack.length - 1].stage = "right";
+        if (node.left !== null) {
+          stack.push({ node: node.left, stage: "left" });
+        }
+      } else if (stage === "right") {
+        stack[stack.length - 1].stage = "node";
+        if (node.right !== null) {
+          stack.push({ node: node.right, stage: "left" });
+        }
+      } else if (stage === "node") {
+        stack.pop();
+        values.push(node.value);
+      }
+    }
     return values;
   };
   // Only change code above this line