算法 - 深度优先搜索和广度优先搜索 - 深度优先 - 非递归

void dfs(TreeNode *pRoot)
{
        if (!pRoot)  return;
        stack<TreeNode*> s;
        TreeNode* cur = pRoot;
        while (cur || !s.empty()) {
            while (cur) {
                s.push(cur);
                cur = cur->left;
            }
            cur = s.top();
            cout<<cur.val;
            s.pop();
            cur = cur->right;
        }
        return true;
}