Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.
一颗二叉树，获取从右边看去能看到的每层的第一个节点，就是每层最右侧的节点。
广度优先遍历，做一点小修改就行：
var rightSideView = function(root) {
var result = [];
if (!root)
return result;
var pre = [root];
var now = [];
while (pre.length) {
result.push(pre[0].val);
for(var i = 0;i < pre.length ;i++) {
if (pre[i].right)
now.push(pre[i].right);
if (pre[i].left)
now.push(pre[i].left);
}
pre = now;
now = [];
}
return result;
};
