feat: update ts solution to lc problem: No.0617 (doocs#1441)

Author: thinkasany

solution/0600-0699/0617.Merge Two Binary Trees/README.md

@@ -188,11 +188,11 @@ function mergeTrees(
     root1: TreeNode | null,
     root2: TreeNode | null,
 ): TreeNode | null {
-    if (root1 == null && root2 == null) return null;
-    if (root1 == null) return root2;
-    if (root2 == null) return root1;
-    let left = mergeTrees(root1.left, root2.left);
-    let right = mergeTrees(root1.right, root2.right);
+    if (root1 === null && root2 === null) return null;
+    if (root1 === null) return root2;
+    if (root2 === null) return root1;
+    const left = mergeTrees(root1.left, root2.left);
+    const right = mergeTrees(root1.right, root2.right);
     return new TreeNode(root1.val + root2.val, left, right);
 }
 ```

solution/0600-0699/0617.Merge Two Binary Trees/README_EN.md

@@ -169,11 +169,11 @@ function mergeTrees(
     root1: TreeNode | null,
     root2: TreeNode | null,
 ): TreeNode | null {
-    if (root1 == null && root2 == null) return null;
-    if (root1 == null) return root2;
-    if (root2 == null) return root1;
-    let left = mergeTrees(root1.left, root2.left);
-    let right = mergeTrees(root1.right, root2.right);
+    if (root1 === null && root2 === null) return null;
+    if (root1 === null) return root2;
+    if (root2 === null) return root1;
+    const left = mergeTrees(root1.left, root2.left);
+    const right = mergeTrees(root1.right, root2.right);
     return new TreeNode(root1.val + root2.val, left, right);
 }
 ```

solution/0600-0699/0617.Merge Two Binary Trees/Solution.ts

@@ -16,10 +16,10 @@ function mergeTrees(
     root1: TreeNode | null,
     root2: TreeNode | null,
 ): TreeNode | null {
-    if (root1 == null && root2 == null) return null;
-    if (root1 == null) return root2;
-    if (root2 == null) return root1;
-    let left = mergeTrees(root1.left, root2.left);
-    let right = mergeTrees(root1.right, root2.right);
+    if (root1 === null && root2 === null) return null;
+    if (root1 === null) return root2;
+    if (root2 === null) return root1;
+    const left = mergeTrees(root1.left, root2.left);
+    const right = mergeTrees(root1.right, root2.right);
     return new TreeNode(root1.val + root2.val, left, right);
 }