DFS (Pre/In/Post Traversal)

Key Signals & Indicators

• Path calculations from root to leaf
• Subtree properties or evaluations (post-order validation)
• BST property matching (in-order yields sorted order)

// C++ Tree DFS Pre/In/Post Template
#include <vector>

struct TreeNode {
    int val;
    TreeNode* left;
    TreeNode* right;
};

void preOrderDFS(TreeNode* root, std::vector<int>& path) {
    if (!root) return;
    
    path.push_back(root->val);     // PRE-ORDER
    preOrderDFS(root->left, path);
    preOrderDFS(root->right, path);
}

void inOrderDFS(TreeNode* root, std::vector<int>& path) {
    if (!root) return;
    
    inOrderDFS(root->left, path);
    path.push_back(root->val);     // IN-ORDER
    inOrderDFS(root->right, path);
}

void postOrderDFS(TreeNode* root, std::vector<int>& path) {
    if (!root) return;
    
    postOrderDFS(root->left, path);
    postOrderDFS(root->right, path);
    path.push_back(root->val);     // POST-ORDER
}