1337. The K Weakest Rows in a Matrix
作者:互联网
Given a m * n
matrix mat
of ones (representing soldiers) and zeros (representing civilians), return the indexes of the k
weakest rows in the matrix ordered from the weakest to the strongest.
A row i is weaker than row j, if the number of soldiers in row i is less than the number of soldiers in row j, or they have the same number of soldiers but i is less than j. Soldiers are always stand in the frontier of a row, that is, always ones may appear first and then zeros.
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 for each row is: row 0 -> 2 row 1 -> 4 row 2 -> 1 row 3 -> 2 row 4 -> 5 Rows ordered from the weakest to the 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 for each row is: row 0 -> 1 row 1 -> 4 row 2 -> 1 row 3 -> 1 Rows ordered from the weakest to the strongest are [0,2,3,1]
Constraints:
m == mat.length
n == mat[i].length
2 <= n, m <= 100
1 <= k <= m
matrix[i][j]
is either 0 or 1.
class Solution { public int[] kWeakestRows(int[][] mat, int k) { PriorityQueue<int[]> pq = new PriorityQueue<>((a, b) -> (a[0] == b[0]) ? b[1] - a[1] : b[0] - a[0]); int n = mat.length; for(int i = 0; i < n; i++) { pq.add(new int[]{help(mat[i]), i}); if(pq.size() > k) pq.poll(); } int[] res = new int[k]; while(k > 0) res[--k] = pq.poll()[1]; return res; } public int help(int[] nums) { int hi = nums.length, lo = 0; while(lo < hi) { int mid = lo + (hi - lo) / 2; if(nums[mid] == 1) { lo = mid + 1; } else hi = mid; } return lo; } }
https://leetcode.com/problems/the-k-weakest-rows-in-a-matrix/discuss/496555/Java-Best-Solution-100-TimeSpace-Binary-Search-%2B-Heap
很多细节,首先是pq,因为要返回最weak的(最小)rows,必须得inverse order排列,并且维持k size,才能保证pq里是需要的rows。
然后返回也是逆序返回。
help method是计算这一行的1个数,用binary search,这样能更快,判断表达式是nums[mid] == 1, 如果是,就 lo = mid + 1,否则hi = mid
标签:Rows,mat,int,lo,1337,mid,pq,row,Matrix 来源: https://www.cnblogs.com/wentiliangkaihua/p/14406003.html