[leetcode] 1007. Minimum Domino Rotations For Equal Row
Description
In a row of dominoes, A[i] and B[i] represent the top and bottom halves of the i-th domino. (A domino is a tile with two numbers from 1 to 6 - one on each half of the tile.)
We may rotate the i-th domino, so that A[i] and B[i] swap values.
Return the minimum number of rotations so that all the values in A are the same, or all the values in B are the same.
If it cannot be done, return -1.
Example 1:
Input: A = [2,1,2,4,2,2], B = [5,2,6,2,3,2]
Output: 2
Explanation:
The first figure represents the dominoes as given by A and B: before we do any rotations.
If we rotate the second and fourth dominoes, we can make every value in the top row equal to 2, as indicated by the second figure.
Example 2:
Input: A = [3,5,1,2,3], B = [3,6,3,3,4]
Output: -1
Explanation:
In this case, it is not possible to rotate the dominoes to make one row of values equal.
Note:
- 1 <= A[i], B[i] <= 6
- 2 <= A.length == B.length <= 20000
分析
题目的意思是：给定两个数组，相同位置可以交换，问最少交换多少次使得其中一个数组所有的数相同。标准答案我没有看见，但我自己实现了一个版本，先统计A和B两个数组的众数，然后遍历A和B找到A变成相同数组的需要的次数cnt1，B变成相同数组所需要的次数cnt2，最后返回最小的次数就行了，如果都没有就只能返回-1了哈，比较笨，思路可以借鉴一下哈，如果有想法，可以跟我讨论一下优化的空间。
代码
class Solution:
def minDominoRotations(self, A: List[int], B: List[int]) -> int:
counter_A=collections.Counter(A)
counter_B=collections.Counter(B)
k1,v1=counter_A.most_common(1)[0]
k2,v2=counter_B.most_common(1)[0]
n=len(A)
flag_A=True
flag_B=True
cnt1=0
cnt2=0
for i in range(n):
if(A[i]!=k1 and B[i]!=k1):
flag_A=False
elif(A[i]!=k1 and B[i]==k1):
cnt1+=1
if(B[i]!=k2 and A[i]!=k2):
flag_B=False
elif(B[i]!=k2 and A[i]==k2):
cnt2+=1
if(flag_A and flag_B):
return min(cnt1,cnt2)
elif(flag_A):
return cnt1
elif(flag_B):
return cnt2
else:
return -1