Summary of Binary Tree Algorithms

Basic Algorithms for recording Binary Trees

Binary Tree node structure:

typedef struct TreeNode{    int val;    struct TreeNode *left;    struct TreeNode *right;           }TreeNode,*Node;

1. Traverse

Recursive traversal of forward, center, and backward order:

void pre_order_traversal(TreeNode *root){    if(root! = NULL){        visit(root);        pre_order_traversal(root->left);        pre_order_traversal(root->right);    }}

void in_order_traversal(TreeNode *root){    if(root! = NULL){        pre_order_traversal(root->left);        visit(root);        pre_order_traversal(root->right);    }}

void post_order_traversal(TreeNode *root){    if(root! = NULL){        pre_order_traversal(root->left);        pre_order_traversal(root->right);        visit(root);    }}

Non-recursive traversal of forward, center, and backward orders:

void pre_order_traversal(TreeNode *root){    if(root==NULL)return;    stack<TreeNode> stack;    while(root!=NULL || !stack.empty()){        if(root){            visit(root);            stack.push(root);            root=root->left;        }else{            root=stack.pop();            root=root->right;        }    }}

void in_order_traversal(TreeNode *root){    if(root==NULL)return;    stack<TreeNode> stack;    while(root!=NULL || !stack.empty()){        if(root){            stack.push(root);            root=root->left;        }else{            root=stack.pop();            visit(root);            root=root->right;        }    }}

void post_order_traversal(TreeNode *root){    if(root==NULL)return;    stack<TreeNode> stack;    TreeNode *flag = NULL;    while(root!=NULL || !stack.empty()){        if(root){            stack.push(root);            root=root->left;        }else{            root=stack.top();            if(root->right && root->right != flag){                root=root->right;            }else{                root=stack.pop();                visit(root);                flag=root;                root=NULL;            }        }    }}

Hierarchical traversal:

void level_order_traversal(TreeNode *root){    if(root == NULL)return;    queue<TreeNode> queue;    queue.push(root);    while(!queue.empty()){        root = queue.pop();        visit(root);        if(root->left){            queue.push(root->left);        }        if(root->right){            queue.push(root->right);        }    }}

 

Summary of Binary Tree Algorithms