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+# 19. find corresponding node in two identical DOM tree
+
+### Problem
+
+https://bigfrontend.dev/problem/find-corresponding-node-in-two-identical-DOM-tree
+
+#
+
+### Problem Description
+
+Given two same DOM tree **A**, **B**, and an Element **a** in **A**, find the corresponding Element **b** in **B**.
+
+By **corresponding**, we mean **a** and **b** have the same relative position to their DOM tree root.
+
+_follow up_
+
+This could a problem on general Tree structure with only `children`.
+
+Could you solve it recursively and iteratively?
+
+Could you solve this problem both with special DOM api for better performance?
+
+What are the time cost for each solution?
+
+#
+
+### Recursive Solution
+
+```js
+/**
+ * @param {HTMLElement} rootA
+ * @param {HTMLElement} rootB - rootA and rootB are clone of each other
+ * @param {HTMLElement} nodeA
+ */
+const findCorrespondingNode = (rootA, rootB, targetNode) => {
+  if (rootA === targetNode) {
+    return rootB;
+  }
+
+  for (let i = 0; i < rootA.childNodes.length; i++) {
+    const result = findCorrespondingNode(
+      rootA.childNodes[i],
+      rootB.childNodes[i],
+      targetNode
+    );
+    if (result) {
+      return result;
+    }
+  }
+  return null;
+};
+```
+
+#
+
+### Iterative Solution
+
+```js
+/**
+ * @param {HTMLElement} rootA
+ * @param {HTMLElement} rootB - rootA and rootB are clone of each other
+ * @param {HTMLElement} nodeA
+ */
+const findCorrespondingNode = (rootA, rootB, target) => {
+  let stackA = [rootA];
+  let stackB = [rootB];
+
+  while (stackA.length > 0) {
+    const nodeA = stackA.pop();
+    const nodeB = stackB.pop();
+
+    if (nodeA === target) {
+      return nodeB;
+    }
+
+    stackA.push(...nodeA.childNodes);
+    stackB.push(...nodeB.childNodes);
+  }
+
+  return;
+};
+```
+
+#
+
+### Solution with DOM API `parentNode`
+
+```js
+/**
+ * @param {HTMLElement} rootA
+ * @param {HTMLElement} rootB - rootA and rootB are clone of each other
+ * @param {HTMLElement} nodeA
+ */
+const findCorrespondingNode = (rootA, rootB, target) => {
+  const path = [];
+  let node = target;
+  while (node !== rootA) {
+    const parentNode = node.parentNode;
+    const childNodes = Array.from(parentNode.childNodes);
+    path.push(childNodes.indexOf(node));
+    node = parentNode;
+  }
+
+  return path.reduceRight((node, index) => node.childNodes[index], rootB);
+};
+```
+# 
+
+### Usage 
+
+```js
+const rootA = {
+  value: "A",
+  childNodes: [
+    {
+      value: "B",
+      childNodes: [
+        {
+          value: "C",
+          childNodes: [],
+        },
+      ],
+    },
+  ],
+};
+
+const rootB = {
+  value: "A",
+  childNodes: [
+    {
+      value: "B",
+      childNodes: [
+        {
+          value: "C",
+          childNodes: [],
+        },
+      ],
+    },
+  ],
+};
+
+const targetNode = rootA.childNodes[0].childNodes[0];
+
+console.log(findCorrespondingNode(rootA, rootB, targetNode));
+```
+
+
+#
+
+### Explanation
+
+Let's break down the `findCorrespondingNode` function and its usage:
+
+1. **Function Definition**: The `findCorrespondingNode` function takes three arguments: `nodeA`, `nodeB`, and `targetNode`. It's designed to find a node in `nodeB` that corresponds to `targetNode` in `nodeA`, assuming `nodeA` and `nodeB` have the same structure.
+
+2. **Base Cases**: If `nodeA` is the `targetNode`, it returns `nodeB`. If `nodeA` has no child nodes, it returns `null` because there's no corresponding node in `nodeB`.
+
+3. **Recursion**: If `nodeA` is not the `targetNode` and it has child nodes, it recursively calls `findCorrespondingNode` for each pair of child nodes in `nodeA` and `nodeB`. If a recursive call returns a non-null result, it returns that result.
+
+4. **Usage**: The usage example creates two identical tree structures `nodeA` and `nodeB`, each with a root node and a single child node that also has a single child node. It then calls `findCorrespondingNode` with `nodeA`, `nodeB`, and the first child node of `nodeA` as the `targetNode`.
+
+5. **Output**: The output of the function call is the first child node of `nodeB`, which corresponds to the `targetNode` in `nodeA`. This is logged to the console.
+
+This `findCorrespondingNode` function can be used to find corresponding nodes in two tree structures that have the same structure. It uses a depth-first search strategy, checking the current node before checking the child nodes.
+
+#
+
+### Reference
+
+[Problem Discuss](https://bigfrontend.dev/problem/find-corresponding-node-in-two-identical-DOM-tree/discuss)