英文:
while loop condtion, difference between not equal and greater than
问题
以下是您提供的内容的翻译部分：
我正在解决一个问题，即判断一个整数是否为回文数。我的逻辑是将其转换为字符串，然后设置第一个和最后一个索引。我循环遍历每个第一个和最后一个索引，如果它们是回文数，则值应该匹配。在循环中，我将第一个索引增加一，将最后一个索引减少一。所以最终它们会在中间相遇。我最初的循环条件是如果两者的索引不相同。但是这会导致字符串索引超出界限异常。但是当我将循环条件更改为只要起始小于结束就可以时，它就可以工作了。
public boolean isPalindrome(int x) {
if(x < 0) {
return false;
}
String val = String.valueOf(x);
int end = val.length()-1;
int start = 0;
while(start != end) {
if(val.charAt(start) != val.charAt(end)) {
return false;
}
start++;
end--;
}
return true;
}
}
当我执行以下操作时，它可以工作：
if(str.charAt(start++) < str.charAt(end--)) return false;
英文:
I'm doing a problem checking whether an integer is a palindrome. The logic is I convert it to string and then set the index of the first and the last. I loop through each first and last index and the values should match if they are palindrome. in the loop I increase the first index by one, I decrease the last index by one. So eventually they will meet in the half. The loop condition I originally had was if the indexes of both are not the same. but this gives me String index out of bounds exception. But then when I changed it to loop through as long as start is smaller than the end, it works.
public boolean isPalindrome(int x) {
if(x < 0) {
return false;
}
String val = String.valueOf(x);
int end = val.length()-1;
int start = 0;
while(start != end) {
if(val.charAt(start) != val.charAt(end)) {
return false;
}
start++;
end--;
}
return true;
}
}
it works when I do
if(str.charAt(start++) < str.charAt(end--)) return false;
答案1
得分: 3
如果长度是偶数，就会出现问题。例如，如果长度是4，你会得到以下运行结果：
开始 | 结束
0 3
1 2
2 1
3 0
4 -1 <--- 错误
因为在整个过程中，不等式条件始终为真。
英文:
You have problem if the length is even number. For example if length is 4, you will have this run:
START | END
0 3
1 2
2 1
3 0
4 -1 <--- error
as during whole time the condition of not-equality is true.
答案2
得分: 0
问题是由于数字中的数字个数：
例如，对于 1221，start 和 end 永远不会在中间相遇：
- 迭代 1：start = 0，end = 3
- 迭代 2：start = 1，end = 2
- 迭代 3：start = 2，end = 1
...
事实上，当你执行以下操作时：“它起作用”
if(str.charAt(start++) < str.charAt(end--)) return false;
纯粹是偶然。
你应该只需将 while 条件更改为：
while(start < end) {
英文:
The issue is due to the number of digit in the number :
for example, for 1221, start and end will never meet in the middle :
- iteration 1 : start = 0, end = 3
- iteration 2 : start = 1, end = 2
- iteration 3 : start = 2, end = 1
...
The fact that "it works" when you do :
if(str.charAt(start++) < str.charAt(end--)) return false;
is by chance.
You should just change the while condition to :
while(start < end) {
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