【LeetCode】113. Path Sum II

Path Sum II

Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum.

For example:
Given the below binary tree and

sum = 22

,

5
/ \
4   8
/   / \
11  13  4
/  \    / \
7    2  5   1

return

[
[5,4,11,2],
[5,8,4,5]
]

这题是在Path Sum的基础上稍作修改。

与上题增加的动作是保存当前stack中路径的加和curSum。

当curSum等于sum时，将cur加入ret。

/**
* Definition for binary tree
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
vector<vector<int> > pathSum(TreeNode *root, int sum) {
vector<vector<int> > ret;
if(!root)
return ret;

stack<TreeNode*> stk;
vector<int> cur;
cur.push_back(root->val);
int curSum = root->val;
unordered_map<TreeNode*, bool> visited;
stk.push(root);
visited[root] = true;

while(!stk.empty())
{
TreeNode* top = stk.top();
if(!top->left && !top->right)
{//leaf
if(curSum == sum)
ret.push_back(cur);
}

if(top->left && visited[top->left] == false)
{
stk.push(top->left);
visited[top->left] = true;
cur.push_back(top->left->val);
curSum += top->left->val;
continue;
}
if(top->right && visited[top->right] == false)
{
stk.push(top->right);
visited[top->right] = true;
cur.push_back(top->right->val);
curSum += top->right->val;
continue;
}

stk.pop();
curSum -= top->val;
cur.pop_back();
}
return ret;
}
};