c++ 实现递归/非递归二叉树遍历_c++非递归遍历二叉树-优快云博客

本文深入探讨了二叉树的遍历方法，包括前序、中序和后序遍历的递归与非递归实现。通过具体的代码示例，详细解释了每种遍历方式的工作原理及其实现细节。

TreeNode数据结构

struct TreeNode {
	int val;
	TreeNode * left;
	TreeNode * right;
	TreeNode(const int & _val = int(), TreeNode * _left = nullptr, TreeNode * _right = nullptr)
		: val(_val), left(_left), right(_right) {}
};

递归

void preOrder(TreeNode * root) {
	if (nullptr == root) {
		return;
	}
	cout << root->val << ' ';
	preOrder(root->left);
	preOrder(root->right);
}
void inOrder(TreeNode * root) {
	if (nullptr == root) {
		return;
	}
	preOrder(root->left);
	cout << root->val << ' ';
	preOrder(root->right);
}
void postOrder(TreeNode * root) {
	if (nullptr == root) {
		return;
	}
	preOrder(root->left);
	preOrder(root->right);
	cout << root->val << ' ';
}

非递归方法（两种）

const int capacity = 1 << 16;
void preOrder(TreeNode * root) {
	TreeNode * stk[capacity];
	TreeNode * tmp = root;
	int top = 0;
	while (tmp || top) {
		while (tmp) {
			cout << tmp->val << ' ';
			stk[top++] = tmp;
			tmp = tmp->left;
		}
		if (top) {
			tmp = stk[--top];
			tmp = tmp->right;
		}
	}
}
void inOrder(TreeNode * root) {
	TreeNode * stk[capacity];
	TreeNode * tmp = root;
	int top = 0;
	while (tmp || top) {
		while (tmp) {
			stk[top++] = tmp;
			tmp = tmp->left;
		}
		if (top) {
			tmp = stk[--top];
			cout << tmp->val << ' ';
			tmp = tmp->right;
		}
	}
}
void postOrder(TreeNode * root) {
	TreeNode * stk[capacity];
	TreeNode * tmp = root;
	int top = 0;
	stk[top++] = tmp;
	stk[top++] = tmp;
	while (top) {
		tmp = stk[--top];
		if (top && tmp == stk[top - 1]) {
			if (tmp->right) {
				stk[top++] = tmp->right;
				stk[top++] = tmp->right;
			}
			if (tmp->left) {
				stk[top++] = tmp->left;
				stk[top++] = tmp->left;
			}
		}
		else {
			cout << tmp->val << ' ';
		}
	}
}

#define pitpb pair<TreeNode*, bool>
const int capacity = 1 << 16;
void preOrder(TreeNode * root) {
	pitpb stk[capacity];
	int top = 0;
	stk[top++] = pitpb(root, false);
	while (top) {
		pitpb tmp = stk[--top];
		if (!tmp.first) {
			continue;
		}
		if (tmp.second) {
			cout << tmp.first->val << ' ';
		}
		else {
			stk[top++] = pitpb(tmp.first->right, false);
			stk[top++] = pitpb(tmp.first->left, false);
			stk[top++] = pitpb(tmp.first, true);
		}
	}
}
void inOrder(TreeNode * root) {
	pitpb stk[capacity];
	int top = 0;
	stk[top++] = pitpb(root, false);
	while (top) {
		pitpb tmp = stk[--top];
		if (!tmp.first) {
			continue;
		}
		if (tmp.second) {
			cout << tmp.first->val << ' ';
		}
		else {
			stk[top++] = pitpb(tmp.first->right, false);
			stk[top++] = pitpb(tmp.first, true);
			stk[top++] = pitpb(tmp.first->left, false);
		}
	}
}
void postOrder(TreeNode * root) {
	pitpb stk[capacity];
	int top = 0;
	stk[top++] = pitpb(root, false);
	while (top) {
		pitpb tmp = stk[--top];
		if (!tmp.first) {
			continue;
		}
		if (tmp.second) {
			cout << tmp.first->val << ' ';
		}
		else {
			stk[top++] = pitpb(tmp.first, true);
			stk[top++] = pitpb(tmp.first->right, false);
			stk[top++] = pitpb(tmp.first->left, false);
		}
	}
}