lintcode-medium-Kth Smallest Number in Sorted Matrix

4

[
[1 ,5 ,7],
[3 ,7 ,8],
[4 ,8 ,9],
]

5

public class Solution {
/**
* @param matrix: a matrix of integers
* @param k: an integer
* @return: the kth smallest number in the matrix
*/
public int kthSmallest(int[][] matrix, int k) {
// write your code here

if(matrix == null || matrix.length == 0 || matrix[0] == null || matrix[0].length == 0)
return 0;

int m = matrix.length;
int n = matrix[0].length;
k--;

if(k < 0 || k > m * n - 1)
return 0;

PriorityQueue<point> queue = new PriorityQueue<point>(n, new Comparator<point>(){
public int compare(point p1, point p2){
return p1.val - p2.val;
}

});

for(int i = 0; i < n; i++){
queue.offer(new point(0, i, matrix[0][i]));
}

for(int i = 0; i < k; i++){
point temp = queue.poll();

if(temp.row + 1 < m){
queue.offer(new point(temp.row + 1, temp.col, matrix[temp.row + 1][temp.col]));
}
}

return queue.poll().val;
}

class point{
int row;
int col;
int val;

public point(int row, int col, int val){
this.row = row;
this.col = col;
this.val = val;
}
}
}