124. 二叉树中的最大路径和
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode() : val(0), left(nullptr), right(nullptr) {}
* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
* TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
* };
*/
class Solution {
public:
int ans = -1001;
int dfs(TreeNode* root,int& ans) {
if(!root)
return 0;
int l_val = dfs(root->left,ans);
int r_val = dfs(root->right,ans);
ans = max(ans,l_val+r_val+root->val);
return max(max(l_val,r_val)+root->val,0);
}
int maxPathSum(TreeNode* root) {
dfs(root,ans);
return ans;
}
};
437. 路径总和 III
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode() : val(0), left(nullptr), right(nullptr) {}
* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
* TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
* };
*/
class Solution {
public:
int ans=0;
unordered_map<long long, int> cnt{{0,1}};
void backtracking(TreeNode* node, long long s, int targetSum) {
if(!node) {
return;
}
s+=node->val;
ans += cnt.contains(s-targetSum) ? cnt[s-targetSum] : 0;
cnt[s]++;
backtracking(node->left,s,targetSum);
backtracking(node->right,s,targetSum);
cnt[s]--;
}
int pathSum(TreeNode* root, int targetSum) {
backtracking(root,0,targetSum);
return ans;
}
};
199. 二叉树的右视图
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode() : val(0), left(nullptr), right(nullptr) {}
* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
* TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
* };
*/
class Solution {
public:
vector<int> res;
void dfs(TreeNode* node,int depth) {
if(!node) {
return;
}
if(depth==res.size())
res.push_back(node->val);
dfs(node->right,depth+1);
dfs(node->left,depth+1);
}
vector<int> rightSideView(TreeNode* root) {
dfs(root,0);
return res;
}
};