Testing2 Solution - Intro to Computer ScienceYouTube↗  IA↗(long shot)
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So here's the answer. The result of the first expression
答案如下 第一个选项的结果始终等于0
is always 0. No matter what string s is, we
不管 s 字符串是什么
always find s at the beginning of itself. So, if
我们始终可以在该字符串的开头找到 s
we think of s as any string. If we search for
如果我们把 s 看作是任意字符串 比如我们在 hello 中搜索字符串 hello
the string hello, in hello, well, we're going to find hello
我们会在 hello 的开始位置找到 hello
at the beginning of hello, and that's position 0, that's
即在第0个位置查找到
what fun will return, no matter what string s is,
这是比较有趣的地方 不管 s 字符串是什么
the result of s.find s will always be 0. The result
s.find 的结果将总是0
of s.find passing in the string s, will only
如果 s 字符串以字母 s 开头 通过 s.find 在 s 字符串进行查找
be 0, if s started with the letter s. So
其结果只会是0
this is not always true. The third example always is
所以这个选项并不总是正确的 第三个选项是正确的
true, so here we have the string s, that's a
这是 s 字符串
string with one character s, and what we're trying
这个字符串只有一个字符 s
to find in it is the string s. Well, we
我们想从该字符串中找到字符串 s
find that at position 0. So that's the result find
发现该字符所在位置是第0个位置
we'll produce. The fourth one gets a little more tricky.
这就是我们通过 find 查找到的结果 第四个选项稍微有些复杂
So here we're looking in the string s. We're looking for the
我们将在这个 s 字符串中进行查找
empty string. Remember the definition of find says it will give us
查找的内容是空字符串 注意 find 的定义是给出该字符串第一次出现的位置
the first occurrence where that string appears. Well the empty string appears
空字符串确实出现在 s 字符串中
in s. We don't actually see it, but it's there. We found
事实上我们看不到 但是它确实存在 我们查找到了空字符串
the empty string. There's no string there no matter what s is.
不管 s 字符串是什么 有没有字符串存在
We can find the empty string in it, because we don't need
我们会查找到其中的空字符串
any string to find the empty string. So the result of s.find
因为我们不需要任何字符串来查找空字符串
passing an empty string, will always be 0, no matter what the
因此不管 s 字符串是什么 s.find 对空字符串的查找结果将始终是0
string s is. So the final one is also always
最后一个选项的结果也始终是0
0. And the reason for this, is when we search
原因是 当我们在 s 字符串中查找 s + ！！！时
in s for the string s plus ! ! , well, no matter what s is. So even if it
不管 s 字符串是什么
was a string that already included ! ! . So
即使是已经包含了 ！！！的 s 字符串
let's suppose that's the value of s. What we're trying
我们假设这就是 s 的值
to find is now s plus ! ! . So
现在我们试图查找的是 s + ！！！
that's going to be what we had before, plus three more
就是在原有的字符串基础上再加上！！！
exclamation points. Searching for that within the string s
在 s 字符串中查找这个
will never be found. And we know it can't be
结果是永远也找不到的
found because this string is actually longer than the
我们知道之所以找不到是因为该字符串
string s that we started with. So the result of
比原字符串 s 长
this expression is always going to be -1. That means
所以查找的结果将是 -1
the string was never found. We add 1 to that,
这说明没有找到该字符串
we get 0. That's why this expression will always evaluate
我们在这基础上加1 结果是0
to 0, no matter what the value of s is.
这就是为什么无论 s 的值是什么 这个选项始终为0的原因
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