剑指offer25 二叉树中和为某一直的路径

 先序遍历

class Solution {
public:
    vector<vector<int> > FindPath(TreeNode* root,int expectNumber) {
        vector<vector<int> > result;
        if(root == NULL)
            return result;
        vector<int> path;
        FindPathCore(root,expectNumber,0,path,result);
        return result;
    }
    void FindPathCore(TreeNode* root,int expectNumber,int sum,vector<int> &path,vector<vector<int> > &result){
        sum += root -> val;
        path.push_back(root -> val);
        if(sum == expectNumber && isleaf(root)){
            result.push_back(path);
        }
        if(root->left != NULL)
            FindPathCore(root->left,expectNumber,sum,path,result);
        if(root->right != NULL)
            FindPathCore(root->right,expectNumber,sum,path,result);
        path.pop_back();
    }
    bool isleaf(TreeNode* root){
        if(root->left == NULL && root->right == NULL)
            return true;
        else
            return false;
    }
};

vector<vector<int> > &result如果这里没有用引用，所有的返回值都为定义初始化时的空