Lunski's Clutter

最近上班聽日文歌發現有首不錯聽，小提琴聲讓人感受到油然而生的希望，Shvara吵著說要學，所以就來研究一下。

這首歌在說走到跟男朋友一起經過的大街，想到以前種種，景物依舊，人事已非，但還是因為不想忘記這段回憶而掙扎。[加油啊(吶喊

我想這種感覺就是物の哀れ吧。

最近遇到對聊天有困擾的朋友，所以我買了這本書，並分享筆記給他，如果對他有幫助，也能幫到一樣有困擾的小夥伴們就太好了。

Count the number of prime numbers less than a non-negative number, n.

Example 1:

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Input: n = 10
Output: 4
Explanation: There are 4 prime numbers less than 10, they are 2, 3, 5, 7.

Example 2:

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Input: n = 0
Output: 0

Example 3:

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Input: n = 1
Output: 0

Given two sorted integer arrays nums1 and nums2, merge nums2 into nums1 as one sorted array.

The number of elements initialized in nums1 and nums2 are m and n respectively. You may assume that nums1 has enough space (size that is equal to m + n) to hold additional elements from nums2.

Example 1:

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Input: nums1 = [1,2,3,0,0,0], m = 3, nums2 = [2,5,6], n = 3
Output: [1,2,2,3,5,6]

Example 2:

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Input: nums1 = [1], m = 1, nums2 = [], n = 0
Output: [1]

Implement strStr().

Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

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().

Example 1:

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Input: haystack = "hello", needle = "ll"
Output: 2

Example 2:

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Input: haystack = "aaaaa", needle = "bba"
Output: -1

Example 3:

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Input: haystack = "", needle = ""
Output: 0

Constraints:

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0 <= haystack.length, needle.length <= 5 * 10ˆ4

haystack and needle consist of only lower-case English characters.