"Leetcode" Path Sum

Path Sum

Given a binary tree and a sum, determine if the tree has a root-to-leaf path such this adding up all the values along the Path equals the given sum.

For example:
Given the below binary tree sum = 22 and,

              5             /             4   8           /   /           /  4         /  \              7    2      1

Return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.

The problem is depth-first traversal (DFS), which uses variable pathsum to record the sum of nodes in the stack.

The node in the stack is the path from the root node to the current node.

If the current node is a leaf node, check whether Pathsum equals sum.

/** Definition for binary tree * struct TreeNode {* int val; * TreeNode *left; * TreeNode *right; * T Reenode (int x): Val (x), left (null), right (NULL) {} *}; */classSolution { Public:    BOOLHaspathsum (TreeNode *root,intsum) {        if(Root = =NULL)return false; intPathsum =0; Stack<TreeNode*>s; Unordered_set<TreeNode*>visited; //Visit RootS.push (root); Pathsum+ = Root->Val;        Visited.insert (root); //whenever add a node into pathsum, check it        if(Root->left = = NULL && Root->right = =NULL) {//root itself is leaf            if(Pathsum = =sum)return true; }            while(!S.empty ()) {TreeNode* top =S.top (); if(top->Left ) {// have left                if(Visited.find (top->left) = =Visited.end ()) {//Not visited//VisitS.push (top->Left ); Pathsum+ = Top->left->Val; Visited.insert (Top-Left ); //Judge Leaf                    if(Top->left->left = = NULL && Top->left->right = =NULL) {//Leaf                        if(Pathsum = =sum)return true; }                    Continue; }            }            if(top->Right ) {// have right                if(Visited.find (top->right) = =Visited.end ()) {//Not visited//VisitS.push (top->Right ); Pathsum+ = Top->right->Val; Visited.insert (Top-Right ); //Judge Leaf                    if(Top->right->left = = NULL && Top->right->right = =NULL) {//Leaf                        if(Pathsum = =sum)return true; }                    Continue;    }} s.pop (); //no need to go down, popPathsum-= top->Val; }        return false; }};

"Leetcode" Path Sum