using namespace std;
BinaryTreeNode* ConstructCore(int* startPreorder, int* endPreorder, int* startInorder, int* endInorder);
BinaryTreeNode* Construct(int* preorder, int* inorder, int length)
{
if (preorder == NULL || inorder == NULL || length <= 0)
return NULL;
return ConstructCore(preorder, preorder + length - 1,
inorder, inorder + length - 1);
}
BinaryTreeNode* ConstructCore
(
int* startPreorder, int* endPreorder,
int* startInorder, int* endInorder
)
{
// 前序遍历序列的第一个数字是根结点的值
int rootValue = startPreorder[0];
BinaryTreeNode* root = new BinaryTreeNode();
root->m_nValue = rootValue;
root->m_pLeft = root->m_pRight = NULL;
if (startPreorder == endPreorder)
{
if (startInorder == endInorder && *startPreorder == *startInorder)
return root;
else
throw std::exception("Invalid input.");
}
// 在中序遍历中找到根结点的值
int* rootInorder = startInorder;
while (rootInorder <= endInorder && *rootInorder != rootValue)
++rootInorder;
if (rootInorder == endInorder && *rootInorder != rootValue)
throw std::exception("Invalid input.");
int leftLength = rootInorder - startInorder;
int* leftPreorderEnd = startPreorder + leftLength;
if (leftLength > 0)
{
// 构建左子树
root->m_pLeft = ConstructCore(startPreorder + 1, leftPreorderEnd,
startInorder, rootInorder - 1);
}
if (leftLength < endPreorder - startPreorder)
{
// 构建右子树
root->m_pRight = ConstructCore(leftPreorderEnd + 1, endPreorder,
rootInorder + 1, endInorder);
}
return root;
}
// ====================测试代码====================
void Test(char* testName, int* preorder, int* inorder, int length)
{
if (testName != NULL)
printf("%s begins:\n", testName);
printf("The preorder sequence is: ");
for (int i = 0; i < length; ++i)
printf("%d ", preorder[i]);
printf("\n");
printf("The inorder sequence is: ");
for (int i = 0; i < length; ++i)
printf("%d ", inorder[i]);
printf("\n");
try
{
BinaryTreeNode* root = Construct(preorder, inorder, length);
PrintTree(root);
DestroyTree(root);
}
catch (std::exception& exception)
{
printf("Invalid Input.\n");
}
}
// 普通二叉树
// 1
// / \
// 2 3
// / / \
// 4 5 6
// \ /
// 7 8
void Test1()
{
const int length = 8;
int preorder[length] = { 1, 2, 4, 7, 3, 5, 6, 8 };
int inorder[length] = { 4, 7, 2, 1, 5, 3, 8, 6 };
Test("Test1", preorder, inorder, length);
}
// 所有结点都没有右子结点
// 1
// /
// 2
// /
// 3
// /
// 4
// /
// 5
void Test2()
{
const int length = 5;
int preorder[length] = { 1, 2, 3, 4, 5 };
int inorder[length] = { 5, 4, 3, 2, 1 };
Test("Test2", preorder, inorder, length);
}
// 所有结点都没有左子结点
// 1
// \
// 2
// \
// 3
// \
// 4
// \
// 5
void Test3()
{
const int length = 5;
int preorder[length] = { 1, 2, 3, 4, 5 };
int inorder[length] = { 1, 2, 3, 4, 5 };
Test("Test3", preorder, inorder, length);
}
// 树中只有一个结点
void Test4()
{
const int length = 1;
int preorder[length] = { 1 };
int inorder[length] = { 1 };
Test("Test4", preorder, inorder, length);
}
// 完全二叉树
// 1
// / \
// 2 3
// / \ / \
// 4 5 6 7
void Test5()
{
const int length = 7;
int preorder[length] = { 1, 2, 4, 5, 3, 6, 7 };
int inorder[length] = { 4, 2, 5, 1, 6, 3, 7 };
Test("Test5", preorder, inorder, length);
}
// 输入空指针
void Test6()
{
Test("Test6", NULL, NULL, 0);
}
// 输入的两个序列不匹配
void Test7()
{
const int length = 7;
int preorder[length] = { 1, 2, 4, 5, 3, 6, 7 };
int inorder[length] = { 4, 2, 8, 1, 6, 3, 7 };
Test("Test7: for unmatched input", preorder, inorder, length);
}
int main( )
{
Test1();
Test2();
Test3();
Test4();
Test5();
Test6();
Test7();
return 0;
}