求二叉樹中任意兩個結點的距離
阿新 • • 發佈:2017-08-12
case itl wid get ren return roo [] fall
求二叉樹中任意兩個結點的距離
- 計算跟到第一個結點的距離;
- 計算跟到第二個結點的距離;
- 計算lca;
- 計算跟到lca結點的距離;
- 結果為(1) + (2) - 2 * (4),因為重復計算了兩次的從跟到lca結點的距離;
1
class Node(object): def __init__(self, value=0): self.value = value self.left = self.right = None def get_path_length(root, n, path): if not root: return 0 ifroot.value == n: return path else: return get_path_length(root.left, n, path + 1) or get_path_length(root.right, n, path + 1) def find_lca(root, n1, n2): if root is None: return None if root.value == n1 or root.value == n2: return root left = find_lca(root.left, n1, n2) right = find_lca(root.right, n1, n2) if left and right: return root elif left: return left elif right: return right else: return None def find_distance(root, n1, n2): x = get_path_length(root, n1, 0) y = get_path_length(root, n2, 0) lca = find_lca(root, n1, n2).value lca_dis = get_path_length(root, lca, 0) return (x + y) - 2 * lca_dis
2
def get_path_length(root, path, k): # base case handling if root is None: return False path.append(root.value) if root.value == k: return True if ((root.left != None and get_path_length(root.left, path, k)) or (root.right != None and get_path_length(root.right, path, k))): return True # 如果當前結點的值並不是k path.pop() return False def find_distance(root, n1, n2): if root: # 獲取第一個結點的路徑(存儲跟結點到i) path1 = [] get_path_length(root, path1, n1) # 獲取第二個結點的路徑 path2 = [] get_path_length(root, path2, n2) # 找到它們的公共祖先 i = 0 while i < len(path1) and i < len(path2): if path1[i] != path2[i]: break i = i + 1 # 減去重復計算的跟結點到lca部分即為結果 return (len(path1) + len(path2) - 2 * i) else: return 0
test
if __name__ == ‘__main__‘: root = Node(1) root.left = Node(2) root.right = Node(3) root.left.left = Node(4) root.right.right = Node(7) root.right.left = Node(6) root.left.right = Node(5) root.right.left.right = Node(8) dist = find_distance(root, 4, 5) print("Distance between node {} & {}: {}".format(4, 5, dist)) dist = find_distance(root, 4, 6) print("Distance between node {} & {}: {}".format(4, 6, dist)) dist = find_distance(root, 3, 4) print("Distance between node {} & {}: {}".format(3, 4, dist)) dist = find_distance(root, 2, 4) print("Distance between node {} & {}: {}".format(2, 4, dist)) dist = find_distance(root, 8, 5) print("Distance between node {} & {}: {}".format(8, 5, dist))
求二叉樹中任意兩個結點的距離