二叉树中的深搜
目录
试题1：计算布尔二叉树的值
算法原理
解法：递归
代码编写
- 个人版本
cpp
class Solution
{
public:
bool evaluateTree(TreeNode* root)
{
return dfs(root);
}
bool dfs(TreeNode* root)
{
if(root == nullptr)
{
return false;
}
if(root->left == nullptr && root->right == nullptr)
{
return root->val;
}
bool left = dfs(root->left);
bool right = dfs(root->right);
if(root->val == 2)
{
return right | left;
}
else
{
return right & left;
}
}
};- 标准版本
cpp
class Solution
{
public:
bool evaluateTree(TreeNode* root)
{
if(root->left == nullptr) return root->val == 0 ? false : true;
bool left = evaluateTree(root->left);
bool right = evaluateTree(root->right);
return root->val == 2 ? left | right : left & right;
}
};试题2：求根节点到叶节点数字之和
算法原理
解法：递归
代码编写
- 个人版本
cpp
class Solution
{
public:
int sumNumbers(TreeNode* root)
{
int ret = dfs(root, 0);
return ret;
}
int dfs(TreeNode* root, int prenum)
{
if(root == nullptr)
{
return 0;
}
int num = prenum * 10 + root->val;
if(root->left == nullptr && root->right == nullptr)
{
return num;
}
int left = dfs(root->left, num);
int right = dfs(root->right, num);
return left + right;
}
};- 标准版本
cpp
class Solution
{
public:
int sumNumbers(TreeNode* root)
{
return dfs(root, 0);
}
int dfs(TreeNode* root, int presum)
{
presum = presum * 10 + root->val;
if(root->left == nullptr && root->right == nullptr)
return presum;
int ret = 0;
if(root->left) ret += dfs(root->left, presum);
if(root->right) ret += dfs(root->right, presum);
return ret;
}
};试题3：二叉树剪枝
算法原理
解法：递归
代码编写
- 个人版本
cpp
class Solution
{
public:
TreeNode* pruneTree(TreeNode* root)
{
return dfs(root);
}
TreeNode* dfs(TreeNode* root)
{
if(root == nullptr)
{
return root;
}
root->left = dfs(root->left);
root->right = dfs(root->right);
if(root->val == 0 && root->right == nullptr && root->left == nullptr)
{
root = nullptr;
}
return root;
}
};- 标准版本
cpp
class Solution
{
public:
TreeNode* pruneTree(TreeNode* root)
{
if(root == nullptr) return nullptr;
root->left = pruneTree(root->left);
root->right = pruneTree(root->right);
if(root->left == nullptr && root->right == nullptr && root->val == 0)
{
delete root;//防止内存泄漏
root = nullptr;
}
return root;
}
};试题4：验证二叉搜索树
算法原理
解法：递归
代码编写
- 个人版本
cpp
class Solution
{
public:
long long prev = -LLONG_MAX;
bool isValidBST(TreeNode* root)
{
if(root == nullptr)
{
return true;
}
if(!isValidBST(root->left))
{
return false;
}
if(root->val <= prev)
{
return false;
}
prev = root->val;
if(!isValidBST(root->right))
{
return false;
}
else
{
return true;
}
}
};- 标准版本
cpp
class Solution
{
long prev = LONG_MIN;
public:
bool isValidBST(TreeNode* root)
{
if(root == nullptr) return true;
bool left = isValidBST(root->left);
bool cur = false;
if(root->val > prev)
cur = true;
prev = root->val;
bool right = isValidBST(root->right);
return left && right && cur;
}
};- 优化版本
cpp
class Solution
{
long prev = LONG_MIN;
public:
bool isValidBST(TreeNode* root)
{
if(root == nullptr) return true;
bool left = isValidBST(root->left);
//剪枝
if(left == false) return false;
bool cur = false;
if(root->val > prev)
cur = true;
//剪枝
if(cur == false) return false;
prev = root->val;
bool right = isValidBST(root->right);
return left && right && cur;
}
};试题5：二叉搜索树中第k小的元素
算法原理
解法：递归
代码编写
- 个人版本
cpp
class Solution
{
int count;
int ret;
public:
int kthSmallest(TreeNode* root, int k)
{
count = k;
ret = 0;
dfs(root);
return ret;
}
void dfs(TreeNode* root)
{
if(root == nullptr)
{
return;
}
dfs(root->left);
count--;
if(count == 0)
{
ret = root->val;
return;
}
dfs(root->right);
}
};- 标准版本
cpp
class Solution
{
int count;
int ret;
public:
int kthSmallest(TreeNode* root, int k)
{
count = k;
dfs(root);
return ret;
}
void dfs(TreeNode* root)
{
if(root == nullptr || count == 0) return;
dfs(root->left);
count--;
if(count == 0) ret = root->val;
dfs(root->right);
}
};试题6：二叉树的所有路径
算法原理
解法：递归
代码编写
- 个人版本
cpp
class Solution
{
vector<string> ret;
public:
vector<string> binaryTreePaths(TreeNode* root)
{
string path;
dfs(root, path);
return ret;
}
void dfs(TreeNode* root, string path)
{
if(root == nullptr)
{
return;
}
if(root->left == nullptr && root->right == nullptr)
{
path += to_string(root->val);
ret.push_back(path);
}
else
{
path += to_string(root->val) + "->";
}
dfs(root->left, path);
dfs(root->right,path);
}
};- 标准版本
cpp
class Solution
{
vector<string> ret;
public:
vector<string> binaryTreePaths(TreeNode* root)
{
string path;
if(root == nullptr) return ret;
dfs(root, path);
return ret;
}
void dfs(TreeNode* root, string path)
{
path += to_string(root->val);
if(root->left == nullptr && root->right == nullptr)
{
ret.push_back(path);
return;
}
path += "->";
//剪枝
if(root->left) dfs(root->left, path);//回溯
if(root->right) dfs(root->right,path);
}
};