二叉树：二叉树的所有路径，回溯
方便理解的版本：
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
vector<string> binaryTreePaths(TreeNode* root) {
vector<string> result;
vector<int> path;
if(root == NULL)
return result;
dfs(root, result, path);
return result;
}
void dfs(TreeNode *root, vector<string>& result, vector<int>& path)
{
if(root == NULL)
return;
path.push_back(root->val);
if(root->left == NULL && root->right == NULL)
{
string tmp;
for(int i =0; i < path.size() - 1; ++i)
{
tmp += to_string(path[i]);
tmp += "->";
}
tmp += to_string(path[path.size() - 1]);
result.push_back(tmp);
}
dfs(root->left, result, path);
dfs(root->right, result, path);
path.pop_back();
}
};
更为简洁的版本：
class Solution {
private:
void traversal(TreeNode* cur, string path, vector<string>& result) {
path += to_string(cur->val); // 中
if (cur->left == NULL && cur->right == NULL) {
result.push_back(path);
return;
}
if (cur->left) traversal(cur->left, path + "->", result); // 左 回溯就隐藏在这里
if (cur->right) traversal(cur->right, path + "->", result); // 右 回溯就隐藏在这里
}
public:
vector<string> binaryTreePaths(TreeNode* root) {
vector<string> result;
string path;
if (root == NULL) return result;
traversal(root, path, result);
return result;
}
};