437. Path Sum III

int pathSum(TreeNode* root, int sum) {
int res=0;
vector<TreeNode*> out;
helper(root,sum,0,out,res);
return res;
}

void helper(TreeNode* root,int sum,int curSum,vector<TreeNode*>& out,int& res){
if(!root) return ;
curSum+=root->val;
out.push_back(root);
if(curSum==sum) res++;
int t=curSum;
for(int i=0;i<out.size()-1;++i){
t-=out[i]->val;
if(t==sum)
res++;
}
helper(root->left,sum,curSum,out,res);
helper(root->right,sum,curSum,out,res);
out.pop_back();
}

int pathSum(TreeNode* root, int sum) {
unordered_map<int,int>m;
m[0]=1;
return helper(root,sum,0,m);
}
int helper(TreeNode* root,int sum,int curSum,unordered_map<int,int>& m){
if(!root) return 0;
curSum+=root->val;
int res=m[curSum-sum];
++m[curSum];
res+=helper(root->left,sum,curSum,m)+helper(root->right,sum,curSum,m);
--m[curSum];
return res;
}