【遍历二叉树】05二叉树的层次遍历II【Binary Tree Level Order Traversal II】
就把vector改成用栈类存放层次遍历的一层的序列
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给定一个二叉树,自底向上的返回他的层次遍历的节点的values。(提示,从左到右,一层一层的遍历,但是这里是从叶子节点到根节点)
例如:
给定一个二叉树 {3,9,20,#,#,15,7}
,
3 / \ 9 20 / \ 15 7
返回的层次遍历的结果是:
[ [15,7] [9,20], [3], ]
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Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from left to right, level by level from leaf to root).
For example:
Given binary tree {3,9,20,#,#,15,7}
,
3 / \ 9 20 / \ 15 7
return its bottom-up level order traversal as:
[ [15,7] [9,20], [3], ]
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test.cpp:
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#include <iostream>
#include <cstdio> #include <stack> #include <vector> #include "BinaryTree.h" using namespace std; /** * Definition for binary tree * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */ vector<vector<int> > levelOrderBottom(TreeNode *root) { vector<vector<int> > matrix; if(root == NULL) { return matrix; } stack<vector<int> > sv; vector<int> temp; temp.push_back(root->val); /*先把根结点的这一行信息放到栈中*/ sv.push(temp); vector<TreeNode *> path; path.push_back(root); int count = 1; while(!path.empty()) { if(path[0]->left != NULL) { path.push_back(path[0]->left); } if(path[0]->right != NULL) { path.push_back(path[0]->right); } path.erase(path.begin()); count--; if(count == 0) { vector<int> tmp; vector<TreeNode *>::iterator it = path.begin(); for(; it != path.end(); ++it) { tmp.push_back((*it)->val); } sv.push(tmp); count = path.size(); } } /*遍历结果栈*/ while(!sv.empty()) { if(sv.top().size() > 0) { matrix.push_back(sv.top()); } sv.pop(); } return matrix; } // 树中结点含有分叉, // 8 // / \ // 6 1 // / \ // 9 2 // / \ // 4 7 int main() { TreeNode *pNodeA1 = CreateBinaryTreeNode(8); TreeNode *pNodeA2 = CreateBinaryTreeNode(6); TreeNode *pNodeA3 = CreateBinaryTreeNode(1); TreeNode *pNodeA4 = CreateBinaryTreeNode(9); TreeNode *pNodeA5 = CreateBinaryTreeNode(2); TreeNode *pNodeA6 = CreateBinaryTreeNode(4); TreeNode *pNodeA7 = CreateBinaryTreeNode(7); ConnectTreeNodes(pNodeA1, pNodeA2, pNodeA3); ConnectTreeNodes(pNodeA2, pNodeA4, pNodeA5); ConnectTreeNodes(pNodeA5, pNodeA6, pNodeA7); PrintTree(pNodeA1); vector<vector<int> > ans = levelOrderBottom(pNodeA1); for (int i = 0; i < ans.size(); ++i) { for (int j = 0; j < ans[i].size(); ++j) { cout << ans[i][j] << " "; } } cout << endl; DestroyTree(pNodeA1); return 0; } |
输出结果:
4 7 9 2 6 1 8
BinaryTree.h:
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#ifndef _BINARY_TREE_H_
#define _BINARY_TREE_H_ struct TreeNode { int val; TreeNode *left; TreeNode *right; TreeNode(int x) : val(x), left(NULL), right(NULL) {} }; TreeNode *CreateBinaryTreeNode(int value); void ConnectTreeNodes(TreeNode *pParent, TreeNode *pLeft, TreeNode *pRight); void PrintTreeNode(TreeNode *pNode); void PrintTree(TreeNode *pRoot); void DestroyTree(TreeNode *pRoot); #endif /*_BINARY_TREE_H_*/ |
BinaryTree.cpp:
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#include <iostream>
#include <cstdio> #include "BinaryTree.h" using namespace std; /** * Definition for binary tree * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */ //创建结点 TreeNode *CreateBinaryTreeNode(int value) { TreeNode *pNode = new TreeNode(value); return pNode; } //连接结点 void ConnectTreeNodes(TreeNode *pParent, TreeNode *pLeft, TreeNode *pRight) { if(pParent != NULL) { pParent->left = pLeft; pParent->right = pRight; } } //打印节点内容以及左右子结点内容 void PrintTreeNode(TreeNode *pNode) { if(pNode != NULL) { printf("value of this node is: %d\n", pNode->val); if(pNode->left != NULL) printf("value of its left child is: %d.\n", pNode->left->val); else printf("left child is null.\n"); if(pNode->right != NULL) printf("value of its right child is: %d.\n", pNode->right->val); else printf("right child is null.\n"); } else { printf("this node is null.\n"); } printf("\n"); } //前序遍历递归方法打印结点内容 void PrintTree(TreeNode *pRoot) { PrintTreeNode(pRoot); if(pRoot != NULL) { if(pRoot->left != NULL) PrintTree(pRoot->left); if(pRoot->right != NULL) PrintTree(pRoot->right); } } void DestroyTree(TreeNode *pRoot) { if(pRoot != NULL) { TreeNode *pLeft = pRoot->left; TreeNode *pRight = pRoot->right; delete pRoot; pRoot = NULL; DestroyTree(pLeft); DestroyTree(pRight); } } |