diff --git a/problems/0106.从中序与后序遍历序列构造二叉树.md b/problems/0106.从中序与后序遍历序列构造二叉树.md index 487e4f7d..40d75983 100644 --- a/problems/0106.从中序与后序遍历序列构造二叉树.md +++ b/problems/0106.从中序与后序遍历序列构造二叉树.md @@ -684,7 +684,7 @@ class Solution: root.right = self.buildTree(preorder_right, inorder_right) return root -``` +``` 106.从中序与后序遍历序列构造二叉树 @@ -716,7 +716,7 @@ class Solution: root.right = self.buildTree(inorder_right, postorder_right) return root -``` +``` ## Go @@ -816,6 +816,7 @@ var buildTree = function(preorder, inorder) { ## C 106 从中序与后序遍历序列构造二叉树 + ```c int linearSearch(int* arr, int arrSize, int key) { int i; @@ -847,6 +848,7 @@ struct TreeNode* buildTree(int* inorder, int inorderSize, int* postorder, int po ``` 105 从前序与中序遍历序列构造二叉树 + ```c struct TreeNode* buildTree(int* preorder, int preorderSize, int* inorder, int inorderSize){ // 递归结束条件:传入的数组大小为0 @@ -889,5 +891,100 @@ struct TreeNode* buildTree(int* preorder, int preorderSize, int* inorder, int in } ``` +## Swift + +105 从前序与中序遍历序列构造二叉树 + +```swift +class Solution { + func buildTree(_ preorder: [Int], _ inorder: [Int]) -> TreeNode? { + return helper(preorder: preorder, + preorderBegin: 0, + preorderEnd: preorder.count, + inorder: inorder, + inorderBegin: 0, + inorderEnd: inorder.count) + } + + func helper(preorder: [Int], preorderBegin: Int, preorderEnd: Int, inorder: [Int], inorderBegin: Int, inorderEnd: Int) -> TreeNode? { + if preorderBegin == preorderEnd { + return nil + } + + // 前序遍历数组的第一个元素作为分割点 + let rootValue = preorder[preorderBegin] + let root = TreeNode(rootValue) + + + if preorderEnd - preorderBegin == 1 { + return root + } + + var index = 0 // 从中序遍历数组中找到根节点的下标 + if let ind = inorder.firstIndex(of: rootValue) { + index = ind + } + + // 递归 + root.left = helper(preorder: preorder, + preorderBegin: preorderBegin + 1, + preorderEnd: preorderBegin + 1 + index - inorderBegin, + inorder: inorder, + inorderBegin: inorderBegin, + inorderEnd: index) + root.right = helper(preorder: preorder, + preorderBegin: preorderBegin + 1 + index - inorderBegin, + preorderEnd: preorderEnd, + inorder: inorder, + inorderBegin: index + 1, + inorderEnd: inorderEnd) + return root + } +} +``` + +106 从中序与后序遍历序列构造二叉树 + +```swift +class Solution_0106 { + func buildTree(inorder: [Int], inorderBegin: Int, inorderEnd: Int, postorder: [Int], postorderBegin: Int, postorderEnd: Int) -> TreeNode? { + if postorderEnd - postorderBegin < 1 { + return nil + } + + // 后序遍历数组的最后一个元素作为分割点 + let rootValue = postorder[postorderEnd - 1] + let root = TreeNode(rootValue) + + if postorderEnd - postorderBegin == 1 { + return root + } + + // 从中序遍历数组中找到根节点的下标 + var delimiterIndex = 0 + if let index = inorder.firstIndex(of: rootValue) { + delimiterIndex = index + } + + root.left = buildTree(inorder: inorder, + inorderBegin: inorderBegin, + inorderEnd: delimiterIndex, + postorder: postorder, + postorderBegin: postorderBegin, + postorderEnd: postorderBegin + (delimiterIndex - inorderBegin)) + + root.right = buildTree(inorder: inorder, + inorderBegin: delimiterIndex + 1, + inorderEnd: inorderEnd, + postorder: postorder, + postorderBegin: postorderBegin + (delimiterIndex - inorderBegin), + postorderEnd: postorderEnd - 1) + return root + } +} +``` + + + -----------------------