Lintcode: Matrix Zigzag Traversal

Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in ZigZag-order.

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Example
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]

Tags Expand  

先斜上走到顶，再斜下走到底，直到计数器满, 写的时候老是fail，才发现14行for循环i不需要++，循环里面自己加了

注意corner cases, 以斜上为例

如果是

1,2

5,6

9,10

中6的这种情况，下一个点是10，则x = x+2, y=y-1

如果是1这种情况， 下一个点是2，则只需x = x+1

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 m = matrix.length;
        int n = matrix[0].length;
        int count = m*n;
        int[] res = new int[count];
        int x=0, y=0;
        for (int i=0; i<count;) {
            while (x>=0 && y<n) {
                res[i++] = matrix[x--][y++];
            }
            if (i == count) break;
            if (x<0 && y<n) {
                x++;
            }
            else {
                x = x+2;
                y = y-1;
            }
            while (x<m && y>=0) {
                res[i++] = matrix[x++][y--];
            }
            if (i == count) break;
            if (x<m && y<0) {
                y++;
            }
            else {
                x = x-1;
                y = y+2;
            }
        }
        return res;
    }
}