Longest zig-zag path in a binary tree

/*
Logic:
->traversed the tree.
->leaf node alone can't contribute in zig zag maximum path so it will return 0.
->zig-zag path can started from any node and in any direction,so answer
  get's updted at every node.
->Assume that parent of current node is the starting node of zig zag maximum path,
  then reversed direction of child of current node can only contribute in
  zig zag path.so we only returned that path zig zag's.
*/
int ans=0;
int fun(TreeNode* root,char dir){
    if(!root->left && !root->right) return 0;
    int n1=0,n2=0;
    if(root->left) n1=fun(root->left,'l');
    if(root->right) n2=fun(root->right,'r');
    ans=max(ans,max(n1,n2)+1);
    if(root->left && dir=='r') return n1+1;
    if(root->right && dir=='l') return n2+1;
    return 0;
}
class Solution {
public:
    int longestZigZag(TreeNode* root) {
        ans=0;
        if(!root) return 0;
        fun(root,'c');
        return ans;
    }
};