广度优先搜索是从某一节点开始，搜索与其线连接的所有节点，按照广度方向像外扩展，直到不重复遍历所有节点。
深度优先搜索是从某一节点开始，沿着其搜索到的第一个节点不断深入下去，当无法再深入的时候，回溯节点，然后再在回溯中的某一节点开始沿另一个方向深度搜索，直到不重复的遍历所有节点。(Breadth first search begins with a node and searches all nodes connected to its line, extending in the direction of the range as far as possible, until all nodes are not repeated.
Depth first search is started from a node, the first node along its search to further down, when not further backtracking node, then a node in the back in the other direction to start the search depth, until not repeated traversal of all nodes.)