題目
給你兩個長度相等的整數數組,返回下面表達式的最大值:
|arr1[i] - arr1[j]| + |arr2[i] - arr2[j]| + |i - j|
其中下標 i,j 滿足 0 <= i, j < arr1.length。
示例 1:
輸入:arr1 = [1,2,3,4], arr2 = [-1,4,5,6]
輸出:13
示例 2:
輸入:arr1 = [1,-2,-5,0,10], arr2 = [0,-2,-1,-7,-4]
輸出:20
思路
最開始看着這題,直接暴力雙重循環,那必須超時啊,最後發現這是一道數學題,首先看條件式|arr1[i] - arr1[j]| + |arr2[i] - arr2[j]| + |i - j|,我們直接將這個式子展開,會有8個不同的表達式,然後 通過觀察,剩下四個不同的式子,
|arr1[i] - arr1[j]| + |arr2[i] - arr2[j]| + |i - j|
= (arr1[i] + arr2[i] + i) - (arr1[j] + arr2[j] + j)
= (arr1[i] + arr2[i] - i) - (arr1[j] + arr2[j] - j)
= (arr1[i] - arr2[i] + i) - (arr1[j] - arr2[j] + j)
= (arr1[i] - arr2[i] - i) - (arr1[j] - arr2[j] - j)
= -(arr1[i] + arr2[i] + i) + (arr1[j] + arr2[j] + j)
= -(arr1[i] + arr2[i] - i) + (arr1[j] + arr2[j] - j)
= -(arr1[i] - arr2[i] + i) + (arr1[j] - arr2[j] + j)
= -(arr1[i] - arr2[i] - i) + (arr1[j] - arr2[j] - j)
A = arr1[i] + arr2[i] + i
B = arr1[i] + arr2[i] - i
C = arr1[i] - arr2[i] + i
D = arr1[i] - arr2[i] - i
因爲對於在計算的時候,i和j是可以調換的,所以這裏可以先考慮i,j也是i
代碼
class Solution:
def maxAbsValExpr(self, arr1: List[int], arr2: List[int]) -> int:
A=[]
B=[]
C=[]
D=[]
for i in range(len(arr1)):
x,y=arr1[i],arr2[i]
A.append(x+y+i)
B.append(x+y-i)
C.append(x-y+i)
D.append(x-y-i)
a=max(A)-min(A)
b=max(B)-min(B)
c=max(C)-min(C)
d=max(D)-min(D)
return max(a,b,c,d)