build

chapter_divide_and_conquer/build_binary_tree_problem.md

@@ -205,17 +205,70 @@ status: new
 === "JS"
 
     ```javascript title="build_tree.js"
-    [class]{}-[func]{dfs}
+    /* 构建二叉树：分治 */
+    function dfs(preorder, inorder, hmap, i, l, r) {
+        // 子树区间为空时终止
+        if (r - l < 0) return null;
+        // 初始化根节点
+        const root = new TreeNode(preorder[i]);
+        // 查询 m ，从而划分左右子树
+        const m = hmap.get(preorder[i]);
+        // 子问题：构建左子树
+        root.left = dfs(preorder, inorder, hmap, i + 1, l, m - 1);
+        // 子问题：构建右子树
+        root.right = dfs(preorder, inorder, hmap, i + 1 + m - l, m + 1, r);
+        // 返回根节点
+        return root;
+    }
 
-    [class]{}-[func]{buildTree}
+    /* 构建二叉树 */
+    function buildTree(preorder, inorder) {
+        // 初始化哈希表，存储 inorder 元素到索引的映射
+        let hmap = new Map();
+        for (let i = 0; i < inorder.length; i++) {
+            hmap.set(inorder[i], i);
+        }
+        const root = dfs(preorder, inorder, hmap, 0, 0, inorder.length - 1);
+        return root;
+    }
     ```
 
 === "TS"
 
     ```typescript title="build_tree.ts"
-    [class]{}-[func]{dfs}
+    /* 构建二叉树：分治 */
+    function dfs(
+        preorder: number[],
+        inorder: number[],
+        hmap: Map<number, number>,
+        i: number,
+        l: number,
+        r: number
+    ): TreeNode | null {
+        // 子树区间为空时终止
+        if (r - l < 0) return null;
+        // 初始化根节点
+        const root: TreeNode = new TreeNode(preorder[i]);
+        // 查询 m ，从而划分左右子树
+        const m = hmap.get(preorder[i]);
+        // 子问题：构建左子树
+        root.left = dfs(preorder, inorder, hmap, i + 1, l, m - 1);
+        // 子问题：构建右子树
+        root.right = dfs(preorder, inorder, hmap, i + 1 + m - l, m + 1, r);
+        // 返回根节点
+        return root;
+    }
 
-    [class]{}-[func]{buildTree}
+    /* 构建二叉树 */
+    function buildTree(preorder: number[], inorder: number[]): TreeNode | null {
+        // 初始化哈希表，存储 inorder 元素到索引的映射
+        let hmap = new Map<number, number>();
+        for (let i = 0; i < inorder.length; i++) {
+            hmap.set(inorder[i], i);
+        }
+        const root = dfs(preorder, inorder, hmap, 0, 0, inorder.length - 1);
+        return root;
+    }
     ```
 
 === "C"