path sum II.

path_sum_II.cpp

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 *  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]
]

 */
class Solution {
public:
    //recursive find path (root->left/right, sum - root.val)
    //    if sum == 0, and !root->left && !root->right, a path is found
    vector<vector<int> > pathSum(TreeNode *root, int sum) {
        vector<vector<int> > vvInt;
         if (!root)
            return vvInt;
        
        vector<int> vPath;
        
        findPathVector(root, vPath, vvInt, sum);
        return vvInt;
    }
    void findPathVector(TreeNode *root, vector<int> path, vector<vector<int> > &vvInt, int sum) {
        if (!root)
            return;
            
        int newSum = sum - root->val;
        path.push_back(root->val);
        if(!root->right && !root->left) {
            if (newSum == 0 ) //found a root-leaf path
                vvInt.push_back(path);
            return;
        }
        
        if (root->left) 
            findPathVector(root->left, path, vvInt, newSum);
        if (root->right)
            findPathVector(root->right, path, vvInt, newSum);
        return;
    }
};