英文:
Question in regards to a line of the code
问题
在下面的代码片段中，我有一个问题，给定的声明数组的类型是整数。你能解释一下在map[s.charAt(i)]++这一行发生了什么吗？我在理解这个语句时遇到了困难，因为在初始化期间数组的类型是整数，但输入却是字符类型。
public int firstUniqChar(String s)
{
int[] map = new int[128];
for(int i=0; i<s.length(); i++)
map[s.charAt(i)]++;
for(int i=0; i<s.length(); i++)
if(map[s.charAt(i)] == 1)
return i;
return -1;
}
英文:
In the below code snipped I have a question, the given declared array is of type integer.Can you please explain on what is happening at the line map[s.charAt(i)]++. I am having trouble understanding the statement here as the array is of type integer during initialization, but character type are being given as input.
public int firstUniqChar(String s)
{
int[] map = new int[128];
for(int i=0;i<s.length();i++)
map[s.charAt(i)]++;
for(int i=0;i<s.length();i++)
if(map[s.charAt(i)] == 1)
return i;
return -1;
}
答案1
得分: 1
在Java中，假设您有一个int i = 0的变量声明，i++是一个语法糖，用于将1添加到变量值，即i = i + 1。
在您的情况下，您正在将1添加到由s.charAt(i)索引的map数组位置。
假设s是一个String对象，s.charAt(i)返回位置为i（从0开始计数）的char。当Java将char读取为int（用于索引map数组）时，它使用该char的ASCII码。
因此，map[s.charAt(i)]++的作用是将1添加到由字符的ASCII码索引的map数组。
英文:
In java, supposing you have a int i = 0 variable declaration, the i++ is a syntax suggar to sum 1 to variable value, i.e. i = i + 1.
In your case you are summing 1 to an map array position, indexed by s.charAt(i).
Supposing s is a String object, s.charAt(i) returns the char at the i position (0-indexed). When the Java reads the char as a int (to index the map array), is uses the ASCII code of that char.
So, what map[s.charAt(i)]++ does is to sum 1 to the map array indexed by the charactere's ASCII code.
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