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二叉树的递归遍历

递归思路

1. 确定递归函数的参数parameter和返回值
2. 确定终止条件
3. 确定单层递归逻辑

具体代码

CPP

前序遍历

vector<int> res;
void traversal(TreeNode *root){if(!root)return;res.push_back(root->val);traversal(root->left);traversal(root->right);
}

中序遍历

vector<int> res;
void traversal(TreeNode *root){if(!root)return;traversal(root->left);res.push_back(root->val);traversal(root->right);
}

后序遍历

vector<int> res;
void traversal(TreeNode *root){if(!root)return;traversal(root->left);traversal(root->right);res.push_back(root->val);
}

Java

先序遍历：

/*** Definition for a binary tree node.* public class TreeNode {*     int val;*     TreeNode left;*     TreeNode right;*     TreeNode() {}*     TreeNode(int val) { this.val = val; }*     TreeNode(int val, TreeNode left, TreeNode right) {*         this.val = val;*         this.left = left;*         this.right = right;*     }* }*/
class Solution {private List<Integer> res;public Solution() {res = new ArrayList<>();}public List<Integer> preorderTraversal(TreeNode root) {if (root == null) {return res;}res.add(root.val);preorderTraversal(root.left);preorderTraversal(root.right);return res;}
}

后序遍历

/*** Definition for a binary tree node.* public class TreeNode {*     int val;*     TreeNode left;*     TreeNode right;*     TreeNode() {}*     TreeNode(int val) { this.val = val; }*     TreeNode(int val, TreeNode left, TreeNode right) {*         this.val = val;*         this.left = left;*         this.right = right;*     }* }*/
class Solution {private List<Integer> res = new ArrayList<>();public List<Integer> postorderTraversal(TreeNode root) {if (root == null) {return res;}postorderTraversal(root.left);postorderTraversal(root.right);res.add(root.val);return res;}
}

中序遍历

/*** Definition for a binary tree node.* public class TreeNode {*     int val;*     TreeNode left;*     TreeNode right;*     TreeNode() {}*     TreeNode(int val) { this.val = val; }*     TreeNode(int val, TreeNode left, TreeNode right) {*         this.val = val;*         this.left = left;*         this.right = right;*     }* }*/
class Solution {private List<Integer> res = new ArrayList<>();public List<Integer> inorderTraversal(TreeNode root) {if (root == null) {return res;}inorderTraversal(root.left);res.add(root.val);inorderTraversal(root.right);return res;}
}