树的遍历 Tree Traversals

let root = {       val: 1,       left:{         val: 2,         left: {            val: 3,            left: {                val: 5            }         },         right: {            val: 4,            right: {                val: 6            }          }       },       right:{           val: 7,           left: {               val: 8           },           right:{               val: 9,               right: {                   val: 10               }           }       }     };

广度优先遍历 Breadth First Traversal

层级遍历 Level Order

Algorithm Postorder(tree)   1. Visit the root. 先访问根节点   2. Traverse the deeper level, visit child root. call levelorder(node, depth)   3. Continue traverse the deeper level, visit child root. call levelorder(node, depth)   ...

var levelOrder = function(root) {    var orders= [];    levelorder(root, 0)    return orders;        function levelorder(node, depth) {        if (!node) {            return;        }        orders[depth] = orders[depth] || [];        orders[depth].push(node.val);        levelorder(node.left, depth + 1);        levelorder(node.right, depth + 1);    }    };console.warn("levelOrder", levelOrder(root));

Output: "levelorder": [[1], [2, 7], [3, 4, 8, 9], [5, 6, 10]]

深度优先遍历 Depth First Traversals

后序遍历 Postorder (Left, Right, Root)

Algorithm Postorder(tree)   1. Traverse the left subtree, i.e., call Postorder(left-subtree) 首先遍历左子树   2. Traverse the right subtree, i.e., call Postorder(right-subtree) 然后遍历右子树   3. Visit the root. 最后访问根节点

var postorderTraversal = function(root) {      var orders = [];      postorder(root);      return orders;          function postorder(node) {         if (node ) {                if (isValidValue(node.left)) {                    postorder(node.left);                }                        if (isValidValue(node.right)) {                    postorder(node.right);                }                                if (isValidValue(node.val)) {                    orders.push(node.val);                }             }        }                function isValidValue(node) {            return node !== null && node !== undefined && node !== "";        }    };        console.warn("postorder", postorderTraversal(root));

Output: "postorder": [5, 3, 6, 4, 2, 8, 10, 9, 7, 1]

中序遍历 Inorder (Left, Root, Right)

Algorithm Inorder(tree)   1. Traverse the left subtree, i.e., call Inorder(left-subtree) 首先遍历左子树   2. Visit the root. 然后访问根节点   3. Traverse the right subtree, i.e., call Inorder(right-subtree) 最后遍历右子树

var inorderTraversal = function(root) {        var orders = [];        inorder(root);        return orders;            function inorder(node) {            if (node ) {                if (isValidValue(node.left)) {                    inorder(node.left);                }                                if (isValidValue(node.val)) {                    orders.push(node.val);                }                              if (isValidValue(node.right)) {                    inorder(node.right);                }            }        }                function isValidValue(node) {            return node !== null && node !== undefined && node !== "";        }    };        console.warn("inorder", inorderTraversal(root));

Output: "inorder": [5, 3, 2, 4, 6, 1, 8, 7, 9, 10]

前序遍历 Preorder (Root, Left, Right)

Algorithm Preorder(tree)   1. Visit the root. 首先访问根节点   2. Traverse the left subtree, i.e., call Preorder(left-subtree) 然后遍历左子树   3. Traverse the right subtree, i.e., call Preorder(right-subtree) 最后遍历右子树``

var preorderTraversal = function(root) {    var orders = [];    preorder(root);    return orders;    function preorder(node) {        if (node ) {            if (isValidValue(node.val)) {                orders.push(node.val);            }                 if (isValidValue(node.left)) {                preorder(node.left);            }                if (isValidValue(node.right)) {                preorder(node.right);            }        }    }        function isValidValue(node) {        return node !== null && node !== undefined && node !== "";    }};console.warn("preorder", preorderTraversal(root));

>  Output: "preorder" [1, 2, 3, 5, 4, 6, 7, 8, 9, 10]