Matrix Zigzag Traversal

Given a matrix:

[
  [1, 2,  3,  4],
  [5, 6,  7,  8],
  [9,10, 11, 12]
]
return [1, 2, 5, 9, 6, 3, 4, 7, 10, 11, 8, 12]

http://www.lintcode.com/en/problem/matrix-zigzag-traversal/

public class Solution {
    /**
     * @param matrix: a matrix of integers
     * @return: an array of integers
     */ 
    public int[] printZMatrix(int[][] matrix) {
        // write your code here
        if(matrix == null || matrix.length == 0 || matrix[0].length == 0) return null;
        int count = matrix.length * matrix[0].length;
        int n = matrix[0].length;
        int m = matrix.length;
        int[] array = new int[count];
        array[0] = matrix[0][0];
        int lastr = 0, lastc=0;
        int i = 1;
        while(i < count){
            //morve right or move down
            if(lastc + 1 < n || lastr + 1 < m){
                if(lastc + 1 < n){
                    lastc++;
                }else{
                    lastr++;
                }
                array[i++] = matrix[lastr][lastc]; 
            }
            //move to dignaol
            while(lastr + 1 < m && lastc - 1 >= 0 ){

                array[i++] = matrix[++lastr][--lastc];
            }
            //move down or right
            if(lastc + 1 < n || lastr + 1 < m){
                if(lastr + 1 < m){
                    lastr++;
                }else{
                    lastc++;
                }
                array[i++] = matrix[lastr][lastc]; 
            }
            //move dignoal up
            while(lastr - 1 >= 0 && lastc  + 1 < n){

                array[i++] = matrix[--lastr][++lastc];
            }           


        }
        return array;
    }
}