LintCode 401. Kth Smallest Number in Sorted Matrix

http://www.lintcode.com/en/problem/kth-smallest-number-in-sorted-matrix/



Find the kth smallest number in at row and column sorted matrix.
Example
Given k = 4 and a matrix:
[
[1 ,5 ,7],
[3 ,7 ,8],
[4 ,8 ,9],
]
return 5