一步一步写算法（之排序二叉树删除-3）

3 普通节点的删除

3.1 删除的节点没有左子树，也没有右子树

测试用例1：删除节点6

/*
*
*         10          ======>     10
*        /  \                      \
*      6     15                     15
*
*/static void test8()
{TREE_NODE* pTreeNode = NULL;assert(TRUE == insert_node_into_tree(&pTreeNode, 10));assert(TRUE == insert_node_into_tree(&pTreeNode, 6));assert(6 == pTreeNode->left_child->data);assert(TRUE == insert_node_into_tree(&pTreeNode, 15));assert(TRUE == delete_node_from_tree(&pTreeNode, 6));assert(NULL == pTreeNode->left_child);free(pTreeNode->right_child);free(pTreeNode);
}

测试用例2：删除节点15

/*
*
*         10          ======>     10
*        /  \                    /
*      6     15                 6
*
*/static void test9()
{TREE_NODE* pTreeNode = NULL;assert(TRUE == insert_node_into_tree(&pTreeNode, 10));assert(TRUE == insert_node_into_tree(&pTreeNode, 6));assert(TRUE == insert_node_into_tree(&pTreeNode, 15));assert(15 == pTreeNode->right_child->data);assert(TRUE == delete_node_from_tree(&pTreeNode, 15));assert(NULL == pTreeNode->right_child);free(pTreeNode->right_child);free(pTreeNode);
}

那么代码应该怎么编写呢？

STATUS _delete_node_from_tree(TREE_NODE* pTreeNode)
{TREE_NODE* pLeftMax;if(NULL == pTreeNode-> left_child && NULL == pTreeNode->right_child){if(pTreeNode == pTreeNode->parent->left_child)pTreeNode->parent->left_child = NULL;elsepTreeNode->parent->right_child = NULL;}free(pTreeNode);return TRUE;
}

3.2 删除的节点有左子树，没有右子树

测试用例1：测试节点6

/*
*
*         10          ======>     10
*        /                      /
*      6                      3
*     /
*    3
*/static void test10()
{TREE_NODE* pTreeNode = NULL;assert(TRUE == insert_node_into_tree(&pTreeNode, 10));assert(TRUE == insert_node_into_tree(&pTreeNode, 6));assert(TRUE == insert_node_into_tree(&pTreeNode, 3));assert(TRUE == delete_node_from_tree(&pTreeNode, 6));assert(3 == pTreeNode->left_child->data);assert(pTreeNode = pTreeNode->left_child->parent);free(pTreeNode->left_child);free(pTreeNode);
}

测试用例2：删除节点15

/*
*
*         10          ======>     10
*           \                       \
*           15                       12
*            /
*           12
*/static void test11()
{TREE_NODE* pTreeNode = NULL;assert(TRUE == insert_node_into_tree(&pTreeNode, 10));assert(TRUE == insert_node_into_tree(&pTreeNode, 15));assert(TRUE == insert_node_into_tree(&pTreeNode, 12));assert(TRUE == delete_node_from_tree(&pTreeNode, 15));assert(12 == pTreeNode->right_child->data);assert(pTreeNode = pTreeNode->right_child->parent);free(pTreeNode->right_child);free(pTreeNode);
}

添加左子树不为空，右子树为空的处理代码，如下所示：

STATUS _delete_node_from_tree(TREE_NODE* pTreeNode)
{TREE_NODE* pLeftMax;if(NULL == pTreeNode-> left_child && NULL == pTreeNode->right_child){if(pTreeNode == pTreeNode->parent->left_child)pTreeNode->parent->left_child = NULL;elsepTreeNode->parent->right_child = NULL;}else if(NULL != pTreeNode->left_child && NULL == pTreeNode->right_child){pTreeNode->left_child->parent = pTreeNode->parent;if(pTreeNode == pTreeNode->parent->left_child)pTreeNode->parent->left_child = pTreeNode->left_child;elsepTreeNode->parent->right_child = pTreeNode->left_child;}free(pTreeNode);return TRUE;
}

3.3 删除的节点左子树为空，右子树节点不为空

测试用例1：删除数据6

/*
*
*         10          ======>    10
*        /                     /
*      6                      8
*       \
*        8
*/static void test12()
{TREE_NODE* pTreeNode = NULL;assert(TRUE == insert_node_into_tree(&pTreeNode, 10));assert(TRUE == insert_node_into_tree(&pTreeNode, 6));assert(TRUE == insert_node_into_tree(&pTreeNode, 8));assert(TRUE == delete_node_from_tree(&pTreeNode, 6));assert(8 == pTreeNode->left_child->data);assert(pTreeNode = pTreeNode->left_child->parent);free(pTreeNode->left_child);free(pTreeNode);
}

测试用例2：删除数据15

/*
*
*        10          ======>    10
*          \                      \
*           15                     20
*             \
*             20
*/static void test13()
{TREE_NODE* pTreeNode = NULL;assert(TRUE == insert_node_into_tree(&pTreeNode, 10));assert(TRUE == insert_node_into_tree(&pTreeNode, 15));assert(TRUE == insert_node_into_tree(&pTreeNode, 20));assert(TRUE == delete_node_from_tree(&pTreeNode, 15));assert(20 == pTreeNode->right_child->data);assert(pTreeNode = pTreeNode->right_child->parent);free(pTreeNode->right_child);free(pTreeNode);
}

添加左子树为空，右子树不为空的处理情形。代码如下：

STATUS _delete_node_from_tree(TREE_NODE* pTreeNode)
{TREE_NODE* pLeftMax;if(NULL == pTreeNode-> left_child && NULL == pTreeNode->right_child){if(pTreeNode == pTreeNode->parent->left_child)pTreeNode->parent->left_child = NULL;elsepTreeNode->parent->right_child = NULL;}else if(NULL != pTreeNode->left_child && NULL == pTreeNode->right_child){pTreeNode->left_child->parent = pTreeNode->parent;if(pTreeNode == pTreeNode->parent->left_child)pTreeNode->parent->left_child = pTreeNode->left_child;elsepTreeNode->parent->right_child = pTreeNode->left_child;}else if(NULL == pTreeNode->left_child && NULL != pTreeNode->right_child){pTreeNode->right_child->parent = pTreeNode->parent;if(pTreeNode == pTreeNode->parent->left_child)pTreeNode->parent->left_child = pTreeNode->right_child;elsepTreeNode->parent->right_child = pTreeNode->right_child;}free(pTreeNode);return TRUE;
}

3.4 删除的节点左右子树均不为空，不过又要分为两种情形：

1）左节点是删除节点左侧的最大节点（删除节点6）

/*
*
*         10          ======>    10
*        /                     /
*      6                      5
*    /  \                      \
*   5    8                      8
*/static void test14()
{TREE_NODE* pTreeNode = NULL;assert(TRUE == insert_node_into_tree(&pTreeNode, 10));assert(TRUE == insert_node_into_tree(&pTreeNode, 6));assert(TRUE == insert_node_into_tree(&pTreeNode, 5));assert(TRUE == insert_node_into_tree(&pTreeNode, 8));assert(TRUE == delete_node_from_tree(&pTreeNode, 6));assert(5 == pTreeNode->left_child->data);assert(pTreeNode = pTreeNode->left_child->parent);assert( 8 == pTreeNode->left_child->right_child->data);assert(pTreeNode->left_child = pTreeNode->left_child->right_child->parent);free(pTreeNode->left_child->right_child);free(pTreeNode->left_child);free(pTreeNode);
}

2）左节点不是删除节点左侧的最大节点（删除节点5）

/*
*
*         10          ======>    10
*        /                     /
*       5                      4
*      / \                    / \
*     2   6                  2   6
*      \
*       4
*/static void test15()
{TREE_NODE* pTreeNode = NULL;assert(TRUE == insert_node_into_tree(&pTreeNode, 10));assert(TRUE == insert_node_into_tree(&pTreeNode, 5));assert(TRUE == insert_node_into_tree(&pTreeNode, 2));assert(TRUE == insert_node_into_tree(&pTreeNode, 4));assert(TRUE == insert_node_into_tree(&pTreeNode, 6));assert(TRUE == delete_node_from_tree(&pTreeNode, 5));assert(4 == pTreeNode->left_child->data);assert(NULL == pTreeNode->left_child->left_child->right_child);free(pTreeNode->left_child->left_child);free(pTreeNode->left_child->right_child);free(pTreeNode->left_child);free(pTreeNode);
}

那么针对这两种类型，我们的代码究竟应该怎么处理呢？

STATUS _delete_node_from_tree(TREE_NODE* pTreeNode)
{TREE_NODE* pLeftMax;if(NULL == pTreeNode-> left_child && NULL == pTreeNode->right_child){if(pTreeNode == pTreeNode->parent->left_child)pTreeNode->parent->left_child = NULL;elsepTreeNode->parent->right_child = NULL;}else if(NULL != pTreeNode->left_child && NULL == pTreeNode->right_child){pTreeNode->left_child->parent = pTreeNode->parent;if(pTreeNode == pTreeNode->parent->left_child)pTreeNode->parent->left_child = pTreeNode->left_child;elsepTreeNode->parent->right_child = pTreeNode->left_child;}else if(NULL == pTreeNode->left_child && NULL != pTreeNode->right_child){pTreeNode->right_child->parent = pTreeNode->parent;if(pTreeNode == pTreeNode->parent->left_child)pTreeNode->parent->left_child = pTreeNode->right_child;elsepTreeNode->parent->right_child = pTreeNode->right_child;}else{pLeftMax = find_max_node(pTreeNode->left_child);if(pLeftMax == pTreeNode->left_child){if(pTreeNode == pTreeNode->parent->left_child)pTreeNode->parent->left_child = pTreeNode->left_child;elsepTreeNode->parent->right_child = pTreeNode->left_child;pTreeNode->left_child->parent = pTreeNode->parent;pTreeNode->left_child->right_child = pTreeNode->right_child;pTreeNode->right_child->parent = pTreeNode-> left_child;}else{pTreeNode->data = pLeftMax->data;pLeftMax->parent->right_child = pLeftMax->left_child;pLeftMax->left_child->parent = pLeftMax->parent;pTreeNode = pLeftMax;}}free(pTreeNode);return TRUE;
}

结束总结：

上面的过程记录了我们的代码是怎么一步一步走过来的。最后我们给出一份完整的节点删除代码：

STATUS _delete_node_from_tree(TREE_NODE* pTreeNode)
{TREE_NODE* pLeftMax;if(NULL == pTreeNode-> left_child && NULL == pTreeNode->right_child){if(pTreeNode == pTreeNode->parent->left_child)pTreeNode->parent->left_child = NULL;elsepTreeNode->parent->right_child = NULL;}else if(NULL != pTreeNode->left_child && NULL == pTreeNode->right_child){pTreeNode->left_child->parent = pTreeNode->parent;if(pTreeNode == pTreeNode->parent->left_child)pTreeNode->parent->left_child = pTreeNode->left_child;elsepTreeNode->parent->right_child = pTreeNode->left_child;}else if(NULL == pTreeNode->left_child && NULL != pTreeNode->right_child){pTreeNode->right_child->parent = pTreeNode->parent;if(pTreeNode == pTreeNode->parent->left_child)pTreeNode->parent->left_child = pTreeNode->right_child;elsepTreeNode->parent->right_child = pTreeNode->right_child;}else{pLeftMax = find_max_node(pTreeNode->left_child);if(pLeftMax == pTreeNode->left_child){if(pTreeNode == pTreeNode->parent->left_child)pTreeNode->parent->left_child = pTreeNode->left_child;elsepTreeNode->parent->right_child = pTreeNode->left_child;pTreeNode->left_child->parent = pTreeNode->parent;pTreeNode->left_child->right_child = pTreeNode->right_child;pTreeNode->right_child->parent = pTreeNode-> left_child;}else{pTreeNode->data = pLeftMax->data;pLeftMax->parent->right_child = pLeftMax->left_child;pLeftMax->left_child->parent = pLeftMax->parent;           pTreeNode = pLeftMax;}}free(pTreeNode);return TRUE;
}STATUS delete_node_from_tree(TREE_NODE** ppTreeNode, int data)
{TREE_NODE* pTreeNode;TREE_NODE* pLeftMax;if(NULL == ppTreeNode || NULL == *ppTreeNode)return FALSE;pTreeNode = find_data_in_tree_node(*ppTreeNode, data);if(NULL == pTreeNode)return FALSE;if(*ppTreeNode == pTreeNode){if(NULL == pTreeNode->left_child && NULL == pTreeNode->right_child){*ppTreeNode = NULL;}else if(NULL != pTreeNode->left_child && NULL == pTreeNode->right_child){*ppTreeNode = pTreeNode->left_child;pTreeNode->left_child->parent = NULL;}else if(NULL == pTreeNode->left_child && NULL != pTreeNode->right_child){*ppTreeNode = pTreeNode->right_child;pTreeNode->right_child->parent = NULL;}else{pLeftMax = find_max_node(pTreeNode->left_child);if(pLeftMax == pTreeNode->left_child){*ppTreeNode = pTreeNode->left_child;(*ppTreeNode)->right_child = pTreeNode->right_child;(*ppTreeNode)->right_child->parent = *ppTreeNode;(*ppTreeNode)->parent = NULL;}else{pTreeNode->data = pLeftMax->data;pLeftMax->parent->right_child = pLeftMax->left_child;pLeftMax->left_child->parent = pLeftMax->parent;pTreeNode = pLeftMax;}}free(pTreeNode);return TRUE;}return _delete_node_from_tree(pTreeNode);
}

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