树的创建以及树的遍历(递归和非递归方法)

分别用递归和非递归方法遍历树。包含前序遍历，中序遍历，后序遍历。本人觉得构建树的方法也很妙，有了这个方法，直接输入数组转化成树，之后测试代码就方便多了。

     //定义树        function TreeNode (value,left,right) {            this.value = value;            this.left = null;            this.right = null;        }        //把数组转化成树        function arrToTree (arr) {            var tree = [];            tree[0] = new TreeNode(arr[0]);//用数组保存结点，之后添加的时候方便查找是哪个结点的子树            for (var i=1; i < arr.length; i++) {                tree[i] = new TreeNode(arr[i]);                if (i % 2 ==1) {                    if(arr[i] != '') {                        tree[parseInt((i-1)/2)].left = tree[i];//寻找父节点，并判断是左子树还是右子树                    }                 } else {                    if(arr[i] != '') {                        tree[parseInt((i-1)/2)].right = tree[i];                    }                 }             }            return tree[0];        }        //算法1: 前序遍历树        //参数里面放result是一个很好的不会把result每次清空的办法        function preOrder (tree,result) {            if (tree == null) {                return;            }            result.push(tree.value);            preOrder(tree.left,result);            preOrder(tree.right,result);            return result;        }        //算法2: 前序遍历树非递归方法        function preOrder2 (tree) {            var stack = [];            var result = [];            if (tree == null) {                return;            }            stack.push(tree);            while (stack.length > 0) {                var node = stack.pop();                result.push(node.value);                //注意进栈顺序，跟着算法走一遍看看                if(node.right != null) {                    stack.push(node.right);                }                if(node.left != null) {                    stack.push(node.left);                }            }            return result;        }        //var tree = arrToTree([1,2,3,4,5,'',6,7,8,9,'','','','','',6]);        //console.log(preOrder2(tree));        //算法3: 中序遍历递归方法        function midOrder (tree,result) {            if(tree == null) {                return;            }            midOrder (tree.left,result);            result.push(tree.value);            midOrder (tree.right,result);            return result;        }        //var tree = arrToTree([1,2,3,4,5,'',6,7,8,9,'','','','','','','',10]);        //console.log(midOrder(tree,[]));        //算法4: 中序遍历非递归方法        function midOrder2 (tree) {            var stack = [];            var result = [];            var node = tree;            while (stack.length > 0 || node) {                if (node) {                    stack.push(node);                    node = node.left;                  } else {                    var node = stack.pop();                    result.push(node.value);                    node = node.right;                }             }            return result;          }        //算法5: 后序遍历递归算法        function postOrder(tree,result) {            if (tree == null) {                return;            }            postOrder(tree.left,result);            postOrder(tree.right,result);            result.push(tree.value);            return result;        }        //算法6: 后序遍历非递归算法        function postOrder2(node) {            var stack = [];            var result = [];            stack.push(node);            while (stack.length > 0) {                var tmp = stack[stack.length-1];                if (tmp.left && tmp.left != node && tmp.right != node) {                    stack.push(tmp.left);                } else if (tmp.right && tmp.right != node) {                    stack.push(tmp.right);                } else {                    var cnode = stack.pop();                    result.push(cnode.value);                    node = tmp;                }            }            return result;              }        var tree = arrToTree([1,2,3,4,5,'',6,7,8,9,'','','','','','','',10]);        console.log(tree);        console.log(postOrder2(tree));