Implement strStr().
Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.
Example 1:
Input: haystack = "hello", needle = "ll" Output: 2
Example 2:
Input: haystack = "aaaaa", needle = "bba" Output: -1
Clarification:
What should we return when needle
is an empty string? This is a great question to ask during an interview.
For the purpose of this problem, we will return 0 when needle
is an empty string. This is consistent to C's strstr() and Java's indexOf().
解题思路:不许用乘、除和求余实现两数的相除。那就只能用加和减了。正常思路是被除数一个一个的减除数,直到剩下的数比除数小为止,就得到了结果。这样是无法ac的,因为时间复杂度为O(n),比如一个很大的数除1,就很慢。这里我们可以用二分查找的思路,可以说又是二分查找的变种。
class Solution(object): def divide(self, dividend, divisor): """ :type dividend: int :type divisor: int :rtype: int """ flag = (dividend < 0 and divisor > 0) or (dividend > 0 and divisor < 0) sums = 0; count = 0; res = 0 a = abs(dividend); b = abs(divisor) while a >= b: sums = b count = 1 while sums*2 <= a: sums += sums count += count a -= sums res += count if flag: return -res elif res > 2147483647: res = 2147483647 return res