113. Path Sum II

113. 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]]

前序遍历的递归的方法，未改进之前：有点DFS的味道

void findPath(TreeNode* root, int sum,vector<int> &path,vector<vector<int>> &paths,int currentSum) //前序遍历保证的才是先从根节点开始    {          currentSum += root->val;          path.push_back(root->val);          if(currentSum == sum && root->left == NULL && root->right == NULL)              paths.push_back(path);                      if(root->left != NULL)              findPath(root->left,sum,path,paths,currentSum);                     if(root->right != NULL)              findPath(root->right,sum,path,paths,currentSum);                        path.pop_back();        }            vector<vector<int>> pathSum(TreeNode* root, int sum) {        if(NULL == root)              return vector<vector<int>> ();                    vector<vector<int>> paths;          vector<int> path;        int currentSum = 0;          findPath(root,sum,path,paths,currentSum);        return paths;    }

改进之后：

vector<vector<int>> pathSum(TreeNode* root, int sum) {        vector<vector<int> > paths;        vector<int> path;        findPaths(root, sum, path, paths);        return paths;      }void findPaths(TreeNode* node, int sum, vector<int>& path, vector<vector<int> >& paths) {        if (!node) return;        path.push_back(node -> val);        if (!(node -> left) && !(node -> right) && sum == node -> val)            paths.push_back(path);        findPaths(node -> left, sum - node -> val, path, paths);        findPaths(node -> right, sum - node -> val, path, paths);        path.pop_back();    }

void findPath(TreeNode* root, int sum,vector<int> &path,vector<vector<int>> &paths) //前序遍历保证的才是先从根节点开始    {          //currentSum += root->val;          path.push_back(root->val);          if(root->val == sum && root->left == NULL && root->right == NULL)              paths.push_back(path);                      if(root->left != NULL)              findPath(root->left,sum-root->val,path,paths);                     if(root->right != NULL)              findPath(root->right,sum-root->val,path,paths);                        path.pop_back();        }            vector<vector<int>> pathSum(TreeNode* root, int sum) {        if(NULL == root)              return vector<vector<int>> ();                    vector<vector<int>> paths;          vector<int> path;         findPath(root,sum,path,paths);        return paths;    }