java ArrayList 删除第一个元素
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ArrayList Removing first element
提问by Bill Cheng
This is the given question: Given a non-negative number represented as an array of digits,
这是给定的问题：给定一个表示为数字数组的非负数，
add 1 to the number ( increment the number represented by the digits ).
给数字加 1（增加由数字表示的数字）。
The digits are stored such that the most significant digit is at the head of the list.
存储这些数字时，最高有效数字位于列表的开头。
Example:
例子：
If the vector has [1, 2, 3]
如果向量有 [1, 2, 3]
the returned vector should be [1, 2, 4]
返回的向量应该是 [1, 2, 4]
as 123 + 1 = 124.
如 123 + 1 = 124。
This is my code:
这是我的代码：
public class Solution {
public ArrayList<Integer> plusOne(ArrayList<Integer> A) {
int carry = 1;
int length = A.size();
ArrayList result = new ArrayList();
for( int i = length - 1; i >=0; i-- ){
int val = A.get(i) + carry;
result.add(0,val % 10);
carry = val / 10;
}
if (carry == 1){
result.add(0,1);
}
for (int j = 0; j < result.size(); j++){
if(result.get(j).equals(0))
result.remove(j);
else
break;
}
return result;
}
}
However, in the test case: A : [ 0, 6, 0, 6, 4, 8, 8, 1 ]
但是，在测试用例中： A : [ 0, 6, 0, 6, 4, 8, 8, 1 ]
it says my function returns
它说我的函数返回
6 6 4 8 8 2
6 6 4 8 8 2
while the correct answer is
而正确答案是
6 0 6 4 8 8 2
6 0 6 4 8 8 2
I have no idea what is wrong with my code.
我不知道我的代码有什么问题。
Thanks!
谢谢！
采纳答案by Patrick Roberts
if(result.get(j).equals(0))
result.remove(j);
else
break;
This will fail if every other index contains a 0. Here's what happens:
如果所有其他索引都包含 0，这将失败。这是发生的事情：
0 6 0 6 4 8 8 2
^ (j = 0)
The 0 will be removed, and jis incremented by one.
0 将被删除，并j增加 1。
6 0 6 4 8 8 2
^ (j = 1)
Then this 0 is removed as well, skipping the first 6 in your array. To fix this, change the snippet to:
然后这个 0 也被删除，跳过数组中的前 6 个。要解决此问题，请将代码段更改为：
if(result.get(j).equals(0))
result.remove(j--);
else
break;
This compensates for when an index is removed so that jwill not skip the number immediately after any removed 0s.
这会在删除索引时进行补偿，以便j在任何删除的 0 之后不会立即跳过该数字。
回答by Nat
Check out a similar question at Looping through and arraylist and removing elements at specified index
查看循环和数组列表并删除指定索引处的元素中的类似问题
simpler to do just
做起来更简单
while (!result.isEmpty() && result.get(0).equals(0)) {
result.remove(0);
}
This will keep removing the left most 0 until there is no more left most zero to be deleted.
这将继续删除最左边的 0，直到没有更多要删除的最左边的 0。
回答by Kushal
Your last forloop is removing 0from your result ArrayList<Integer>. After removing that loop, you will get perfect output
您的最后一个for循环正在0从您的结果中删除ArrayList<Integer>。删除该循环后，您将获得完美的输出
public static ArrayList<Integer> plusOne(ArrayList<Integer> A) {
int carry = 1;
int length = A.size();
ArrayList result = new ArrayList();
for (int i = length - 1; i >= 0; i--) {
int val = A.get(i) + carry; //2 8
result.add(0, val % 10); // 2 8
carry = val / 10;
}
if (carry == 1) {
result.add(0, 1);
}
// for (int j = 0; j < result.size(); j++) {
// if (result.get(j).equals(0))
// result.remove(j);
// else
// break;
// }
for (boolean isZero = true; isZero; ) {
isZero = result.get(0).equals(0);
if(isZero)
result.remove(0);
}
return result;
}
