问题描述：s型遍历二叉树，或者反s型遍历二叉树
算法分析：层序遍历二叉树只需要一个队列，因为每一层都是从左往右遍历，而s型遍历二叉树就要用两个栈了，因为每次方向相反。
public static void SpiralOrderTraverse(TreeNode t) {
Stack<TreeNode> stack1 = new Stack<>();
Stack<TreeNode> stack2 = new Stack<>();
stack1.push(t);
while (!stack1.isEmpty() || !stack2.isEmpty()) {
while (!stack1.isEmpty()) {
TreeNode tn = stack1.pop();
System.out.print(tn.val + " ");
if (tn.right != null) {
stack2.push(tn.right);
}
if (tn.left != null) {
stack2.push(tn.left);
}
}
while (!stack2.isEmpty()) {
TreeNode tn = stack2.pop();
System.out.print(tn.val + " ");
if (tn.left != null) {
stack1.push(tn.left);
}
if (tn.right != null) {
stack1.push(tn.right);
}
}
}
}
SpiralOrderTraverse，螺旋遍历二叉树，利用两个栈
原文：http://www.cnblogs.com/masterlibin/p/5624975.html