#include <vector>
using namespace std;

class Solution {
public:
    vector<int> findDiagonalOrder(vector<vector<int>>& m) {
        int x=0,y=0;
        bool isup=true;
        vector<int> res;
        res.reserve(m.size());
        #define isout (x<0||x>m.size()||y<0||y>m[0].size())
        do{
            res.push_back(m[x][y]);
            if(isup){
                if(x==0){
                    ++y;
                    isup=false;
                }else{
                    --x;
                    ++y;
                }
            }else{
                if(y==0){
                    ++x;
                    isup=true;
                }else{
                    ++x;
                    --y;
                }
            }
        }while(!(x==m.size()&&y==m[0].size()));
        return res;
    }
};

int main(){

    Solution s;
    s.findDiagonalOrder({{1,2,3},{4,5,6},{7,8,9}});
}