Algorithm --> 判读是否是子树
问题
判断一棵树是否是另一棵树的子树,如图
思路
问题分两步:
- 找值相同的根结点(遍历解决)
- 判断两结点是否包含(递归:值、左孩子、右孩子分别相同)
树节点定义
struct TreeNode { int val; TreeNode *next; TreeNode(int v) : val(v), next(NULL) {} };
代码
bool IsPart(TreeNode *root1, TreeNode *root2) { if (root2 == NULL) return true; if (root1 == NULL) return false; if (root1->val != root2->val) return false; return IsPart(root1->left, root2->left) && IsPart(root1->right, root2->right); } bool IsPartTree(TreeNode *root1, TreeNode *root2) { bool result = false; if (root1 != NULL && root2 != NULL) { if (root1->val == root2->val) result = IsPart(root1, root2); if (!result) result = IsPartTree(root1->left, root2); if (!result) result = IsPartTree(root1->right, root2); } return result; }
执行
#include <iostream> #include <stack> using namespace std; struct TreeNode { int val; TreeNode *left; TreeNode *right; TreeNode(int v) : val(v), left(NULL), right(NULL) {} }; bool IsPart(TreeNode *root1, TreeNode *root2) { if (root2 == NULL) return true; if (root1 == NULL) return false; if (root1->val != root2->val) return false; return IsPart(root1->left, root2->left) && IsPart(root1->right, root2->right); } bool IsPartTree(TreeNode *root1, TreeNode *root2) { bool result = false; if (root1 != NULL && root2 != NULL) { if (root1->val == root2->val) result = IsPart(root1, root2); if (!result) result = IsPartTree(root1->left, root2); if (!result) result = IsPartTree(root1->right, root2); } return result; } TreeNode* createTree1() { TreeNode *root = new TreeNode(1); TreeNode *p1 = new TreeNode(2); TreeNode *p2 = new TreeNode(3); TreeNode *p3 = new TreeNode(4); TreeNode *p4 = new TreeNode(5); root->left = p1; root->right = p2; p2->left = p3; p2->right = p4; return root; } TreeNode* createTree2() { TreeNode *root = new TreeNode(1); TreeNode *p1 = new TreeNode(2); TreeNode *p2 = new TreeNode(3); root->left = p1; root->right = p2; return root; } void deleteTree(TreeNode *root) { if (root != NULL) { delete(root->left); delete(root->right); delete root; root = NULL; } } int main() { TreeNode *root1 = createTree1(); TreeNode *root2 = createTree2(); cout << IsPartTree(root1, root2) << endl; deleteTree(root1); deleteTree(root2); }