Leetcode 498. Diagonal Traverse

// Problem Reference: https://leetcode.com/problems/diagonal-traverse

/*

My sulotion:
Sets up x-y coordinates with the matrix.
So, it only needs to find the start point & end point with their xy coordinate.
Then, it is clear that the answer is moving orderly from start to end on diagonal.
*/

class Solution {
public:
    vector<int> findDiagonalOrder(vector<vector<int>>& matrix) {
        // Store answer.
        vector<int> ans;
        
        // Get bundary value.
        int ymax=matrix.size();
        if (ymax == 0) {
            return ans;
        }
        int xmax=matrix[0].size();

        // Define method moving from start to the end.
        // And distinction between odd and even diagonal is made.
        int xf[2] = {1, -1};
        int yf[2] = {-1, 1};
        
        // Represent the start or end points.
        int xn[2],yn[2];
        
        // Go through all diagonals.
        for (int i=0; i<xmax+ymax-1; i++) {
            
            // Get the point close to the Y axis.
            yn[0] = min(i, ymax-1);
            xn[0] = i - yn[0];

            // Get the point close to the X axis.
            xn[1] = min(i, xmax-1);
            yn[1] = i-xn[1];
            
            // Get the start point due to parity.
            int xp = xn[i%2], yp = yn[i%2];
            
            // Get all nodes needed by moving on the diagonal.
            do {
                ans.push_back(matrix[yp][xp]);
                xp += xf [i%2];
                yp += yf [i%2];
            } while (xp >= 0 && yp >=0 && xp < xmax && yp <ymax);
        }
        return ans;
    }
};