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LeetCode

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Problem

Given an n x n matrix where each of the rows and columns are sorted in ascending order, return the kth smallest element in the matrix.

Note that it is the kth smallest element in the sorted order, not the kth distinct element.

Example 1:

Input: matrix = [[1,5,9],[10,11,13],[12,13,15]], k = 8
Output: 13
Explanation: The elements in the matrix are [1,5,9,10,11,12,13,13,15], and the 8th smallest number is 13

Example 2:

Input: matrix = [[-5]], k = 1
Output: -5

Code

和LeetCode 373题类似

class Solution {
    public int kthSmallest(int[][] matrix, int k) {
        PriorityQueue<int[]> pq = new PriorityQueue<>((a, b) -> (a[0] - b[0]));
        
        for(int i = 0; i < matrix.length; i++) {
            pq.add(new int[]{matrix[i][0], i, 0});
        }
        
        while (!pq.isEmpty() && k-- > 0) {
            int[] curr = pq.poll();
            if(k == 0) return curr[0];
            
            if(curr[2] == matrix[0].length - 1) continue;
            pq.offer(new int[]{matrix[curr[1]][curr[2] + 1], curr[1], curr[2] + 1});
        }
        
        return -1;
    }
}