1 問題

分行從上到下之字行打印二叉樹

比如二叉樹

23 5 1 4 2 3 3 2 1 5 1 4 2 3

?分行從上到下之字行打印二叉樹結果如下

2 5 3 1 4 2 3 3 2 4 1 5 1 2 3

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2 分析

這里我們可以用2個棧（先進后出），先把stack1push根節點，然后把stack全部彈出來，分別push根節點的左節點和右節點到stack2，然后stack2彈出棧里面的每個節點，我們分別把每個節點的右節點和左節點push到stack1,里面去，直到stack1和stack2都是空元素結束循環。

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3 代碼實現

#include <iostream> #include <stack>using namespace std;typedef struct Node {int value;struct Node* left;struct Node* right; } Node;void layer_print(Node *head) {if (head == NULL){std::cout << "head is NULL" << std::endl;return;}std::stack<Node *> stack1, stack2;stack1.push(head);while((stack1.size() != 0) || (stack2.size() != 0)){while (stack1.size() != 0){Node *node = stack1.top();std::cout << node->value << "\t";if (node->left)stack2.push(node->left);if (node->right)stack2.push(node->right);stack1.pop();}std::cout << std::endl;while (stack2.size() != 0){Node *node = stack2.top();std::cout << node->value << "\t";if (node->right)stack1.push(node->right);if (node->left)stack1.push(node->left);stack2.pop();} std::cout << std::endl; } }int main() {/* 2* 3 5 * 1 4 2 3 * 3 2 1 5 1 4 2 3 */Node head1, node1, node2, node3, node4, node5, node6;Node node7, node8, node9, node10, node11, node12, node13, node14;head1.value = 2;node1.value = 3;node2.value = 5;node3.value = 1;node4.value = 4;node5.value = 2;node6.value = 3;node7.value = 3;node8.value = 2;node9.value = 1;node10.value = 5;node11.value = 1;node12.value = 4;node13.value = 2;node14.value = 3;head1.left = &node1;head1.right = &node2;node1.left = &node3;node1.right = &node4;node2.left = &node5;node2.right = &node6;node3.left = &node7;node3.right = &node8;node4.left = &node9;node4.right = &node10;node5.left = &node11;node5.right = &node12;node6.left = &node13;node6.right = &node14;node7.left = NULL;node7.right = NULL;node8.left = NULL;node8.right = NULL;node9.left = NULL;node9.right = NULL;node10.left = NULL;node10.right = NULL;node11.left = NULL;node11.right = NULL;node12.left = NULL;node12.right = NULL;node13.left = NULL;node13.right = NULL;node14.left = NULL;node14.right = NULL;layer_print(&head1);return 0; }

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4 運行結果

2 5 3 1 4 2 3 3 2 4 1 5 1 2 3

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總結

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