[Leetcode] 1337. The K Weakest Rows in a Matrix

You are given an m x n binary matrix mat of 1's (representing soldiers) and 0's (representing civilians). The soldiers are positioned in front of the civilians. That is, all the 1's will appear to the left of all the 0's in each row.

A row i is weaker than a row j if one of the following is true:

• The number of soldiers in row i is less than the number of soldiers in row j.
• Both rows have the same number of soldiers and i < j.

Return the indices of the k weakest rows in the matrix ordered from weakest to strongest.

 

Example 1:

Input: mat = 
[[1,1,0,0,0],
 [1,1,1,1,0],
 [1,0,0,0,0],
 [1,1,0,0,0],
 [1,1,1,1,1]], 
k = 3
Output: [2,0,3]
Explanation: 
The number of soldiers in each row is: 
- Row 0: 2 
- Row 1: 4 
- Row 2: 1 
- Row 3: 2 
- Row 4: 5 
The rows ordered from weakest to strongest are [2,0,3,1,4].

Example 2:

Input: mat = 
[[1,0,0,0],
 [1,1,1,1],
 [1,0,0,0],
 [1,0,0,0]], 
k = 2
Output: [0,2]
Explanation: 
The number of soldiers in each row is: 
- Row 0: 1 
- Row 1: 4 
- Row 2: 1 
- Row 3: 1 
The rows ordered from weakest to strongest are [0,2,3,1].

 

 

0은 시민 1은 병사

병사가 가장 적은 row number 대로 k 개 만큼 정렬하는 문제

 

binary search, minheap 쓰는 방법도 있는데

각 row 합에 대한 내림차순 정렬 후 리스트 만들고 k개만큼 뽑아줬다

 

답)

class Solution:
    def kWeakestRows(self, mat: List[List[int]], k: int) -> List[int]:
        dict_ = {idx : sum(row) for idx, row in enumerate(mat)}
        return [i[0] for i in sorted(dict_.items(), key= lambda x:x[1])][:k]