《剑指offer》第三十二题III:之字形打印二叉树
// 面试题32(三):之字形打印二叉树 // 题目:请实现一个函数按照之字形顺序打印二叉树,即第一行按照从左到右的顺 // 序打印,第二层按照从右到左的顺序打印,第三行再按照从左到右的顺序打印, // 其他行以此类推。 #include <cstdio> #include "BinaryTree.h" #include <stack> void Print(BinaryTreeNode* pRoot) { //整体思路和前两道题很像,先进先出变后进先出 if (pRoot == nullptr) return; std::stack<BinaryTreeNode*> levels[2]; //创建两个栈 int current = 0; //当前为奇数, 从左到右 int next = 1; //下一层为偶数, 从右向左 levels[current].push(pRoot); while (!levels[current].empty() || !levels[next].empty()) { BinaryTreeNode* pNode = levels[current].top(); printf("%d ", pNode->m_nValue); levels[current].pop(); if (current == 0) //当前打印奇数序列, 从左到右 { if (pNode->m_pLeft) levels[next].push(pNode->m_pLeft); if (pNode->m_pRight) levels[next].push(pNode->m_pRight); } else //当前打印偶数序列, 从右到左 { if (pNode->m_pRight) levels[next].push(pNode->m_pRight); if (pNode->m_pLeft) levels[next].push(pNode->m_pLeft); } if (levels[current].empty()) //如果当前节点打印完了 { printf("\n"); current = 1 - current; next = 1 - next; } } }
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// ====================测试代码==================== // 8 // 6 10 // 5 7 9 11 void Test1() { BinaryTreeNode* pNode8 = CreateBinaryTreeNode(8); BinaryTreeNode* pNode6 = CreateBinaryTreeNode(6); BinaryTreeNode* pNode10 = CreateBinaryTreeNode(10); BinaryTreeNode* pNode5 = CreateBinaryTreeNode(5); BinaryTreeNode* pNode7 = CreateBinaryTreeNode(7); BinaryTreeNode* pNode9 = CreateBinaryTreeNode(9); BinaryTreeNode* pNode11 = CreateBinaryTreeNode(11); ConnectTreeNodes(pNode8, pNode6, pNode10); ConnectTreeNodes(pNode6, pNode5, pNode7); ConnectTreeNodes(pNode10, pNode9, pNode11); printf("====Test1 Begins: ====\n"); printf("Expected Result is:\n"); printf("8 \n"); printf("10 6 \n"); printf("5 7 9 11 \n\n"); printf("Actual Result is: \n"); Print(pNode8); printf("\n"); DestroyTree(pNode8); } // 5 // 4 // 3 // 2 void Test2() { BinaryTreeNode* pNode5 = CreateBinaryTreeNode(5); BinaryTreeNode* pNode4 = CreateBinaryTreeNode(4); BinaryTreeNode* pNode3 = CreateBinaryTreeNode(3); BinaryTreeNode* pNode2 = CreateBinaryTreeNode(2); ConnectTreeNodes(pNode5, pNode4, nullptr); ConnectTreeNodes(pNode4, pNode3, nullptr); ConnectTreeNodes(pNode3, pNode2, nullptr); printf("====Test2 Begins: ====\n"); printf("Expected Result is:\n"); printf("5 \n"); printf("4 \n"); printf("3 \n"); printf("2 \n\n"); printf("Actual Result is: \n"); Print(pNode5); printf("\n"); DestroyTree(pNode5); } // 5 // 4 // 3 // 2 void Test3() { BinaryTreeNode* pNode5 = CreateBinaryTreeNode(5); BinaryTreeNode* pNode4 = CreateBinaryTreeNode(4); BinaryTreeNode* pNode3 = CreateBinaryTreeNode(3); BinaryTreeNode* pNode2 = CreateBinaryTreeNode(2); ConnectTreeNodes(pNode5, nullptr, pNode4); ConnectTreeNodes(pNode4, nullptr, pNode3); ConnectTreeNodes(pNode3, nullptr, pNode2); printf("====Test3 Begins: ====\n"); printf("Expected Result is:\n"); printf("5 \n"); printf("4 \n"); printf("3 \n"); printf("2 \n\n"); printf("Actual Result is: \n"); Print(pNode5); printf("\n"); DestroyTree(pNode5); } void Test4() { BinaryTreeNode* pNode5 = CreateBinaryTreeNode(5); printf("====Test4 Begins: ====\n"); printf("Expected Result is:\n"); printf("5 \n\n"); printf("Actual Result is: \n"); Print(pNode5); printf("\n"); DestroyTree(pNode5); } void Test5() { printf("====Test5 Begins: ====\n"); printf("Expected Result is:\n"); printf("Actual Result is: \n"); Print(nullptr); printf("\n"); } // 100 // / // 50 // \ // 150 void Test6() { BinaryTreeNode* pNode100 = CreateBinaryTreeNode(100); BinaryTreeNode* pNode50 = CreateBinaryTreeNode(50); BinaryTreeNode* pNode150 = CreateBinaryTreeNode(150); ConnectTreeNodes(pNode100, pNode50, nullptr); ConnectTreeNodes(pNode50, nullptr, pNode150); printf("====Test6 Begins: ====\n"); printf("Expected Result is:\n"); printf("100 \n"); printf("50 \n"); printf("150 \n\n"); printf("Actual Result is: \n"); Print(pNode100); printf("\n"); } // 8 // 4 12 // 2 6 10 14 // 1 3 5 7 9 11 13 15 void Test7() { BinaryTreeNode* pNode8 = CreateBinaryTreeNode(8); BinaryTreeNode* pNode4 = CreateBinaryTreeNode(4); BinaryTreeNode* pNode12 = CreateBinaryTreeNode(12); BinaryTreeNode* pNode2 = CreateBinaryTreeNode(2); BinaryTreeNode* pNode6 = CreateBinaryTreeNode(6); BinaryTreeNode* pNode10 = CreateBinaryTreeNode(10); BinaryTreeNode* pNode14 = CreateBinaryTreeNode(14); BinaryTreeNode* pNode1 = CreateBinaryTreeNode(1); BinaryTreeNode* pNode3 = CreateBinaryTreeNode(3); BinaryTreeNode* pNode5 = CreateBinaryTreeNode(5); BinaryTreeNode* pNode7 = CreateBinaryTreeNode(7); BinaryTreeNode* pNode9 = CreateBinaryTreeNode(9); BinaryTreeNode* pNode11 = CreateBinaryTreeNode(11); BinaryTreeNode* pNode13 = CreateBinaryTreeNode(13); BinaryTreeNode* pNode15 = CreateBinaryTreeNode(15); ConnectTreeNodes(pNode8, pNode4, pNode12); ConnectTreeNodes(pNode4, pNode2, pNode6); ConnectTreeNodes(pNode12, pNode10, pNode14); ConnectTreeNodes(pNode2, pNode1, pNode3); ConnectTreeNodes(pNode6, pNode5, pNode7); ConnectTreeNodes(pNode10, pNode9, pNode11); ConnectTreeNodes(pNode14, pNode13, pNode15); printf("====Test7 Begins: ====\n"); printf("Expected Result is:\n"); printf("8 \n"); printf("12 4 \n"); printf("2 6 10 14 \n"); printf("15 13 11 9 7 5 3 1 \n\n"); printf("Actual Result is: \n"); Print(pNode8); printf("\n"); DestroyTree(pNode8); } int main(int argc, char* argv[]) { Test1(); Test2(); Test3(); Test4(); Test5(); Test6(); Test7(); return 0; }
分析:举例分析,奇偶数行打印顺序不同,所以下一行压入栈顺序也不同。
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/* struct TreeNode { int val; struct TreeNode *left; struct TreeNode *right; TreeNode(int x) : val(x), left(NULL), right(NULL) { } }; */ class Solution { public: vector<vector<int> > Print(TreeNode* pRoot) { std::stack<TreeNode*> levels[2]; int current = 0; int next = 1; std::vector<vector<int> > printTreeNode; std::vector<int> printTemp; if (pRoot == nullptr) return printTreeNode; levels[current].push(pRoot); while (!levels[current].empty() || !levels[next].empty()) { TreeNode* pNode = levels[current].top(); levels[current].pop(); printTemp.push_back(pNode->val); if (current == 0) { if (pNode->left) levels[next].push(pNode->left); if (pNode->right) levels[next].push(pNode->right); } else { if (pNode->right) levels[next].push(pNode->right); if (pNode->left) levels[next].push(pNode->left); } if (levels[current].empty()) { printTreeNode.push_back(printTemp); printTemp.clear(); current = 1 - current; next = 1 - next; } } return printTreeNode; } };