二叉树基础算法总结

记录一些二叉树的基础算法

二叉树节点结构：

typedef struct TreeNode{

    int val;

    struct TreeNode *left;

    struct TreeNode *right;           

}TreeNode,*Node;

1.遍历

前、中、后序递归遍历：

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);

    }

}

前、中、后序非递归遍历：

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;

            }

        }

    }

}

层次遍历：

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);

        }

    }

}