There are two ways to conduct BFS on tree.
Use recursion to find given level, and print.
/*Function to print level order traversal of tree*/
printLevelorder(tree)
for d = 1 to height(tree)
printGivenLevel(tree, d);
/*Function to print all nodes at a given level*/
printGivenLevel(tree, level)
if tree is NULL then return;
if level is 1, then
print(tree->data);
else if level greater than 1, then
printGivenLevel(tree->left, level-1);
printGivenLevel(tree->right, level-1);
For each node, first the node is visited and then it’s child nodes are put in a FIFO queue.
printLevelorder(tree)
1) Create an empty queue q
2) temp_node = root /*start from root*/
3) Loop while temp_node is not NULL
a) print temp_node->data.
b) Enqueue temp_node’s children (first left then right children) to q
c) Dequeue a node from q and assign it’s value to temp_node
Reference: Level Order Tree Traversal
原文：http://www.cnblogs.com/ireneyanglan/p/4834080.html