[英]how to find second largest index of arraylist in java
I have to write a method that returns the second largest index of an ArrayList of integer values. 我必须编写一个返回整数值ArrayList的第二大索引的方法。
The array list is: 4 8 15 16 23 42 97 56 95 85 63 41 52 99 97 Q 数组列表为:4 8 15 16 23 42 97 56 95 85 63 41 52 99 97 Q
The Q is there to mark the end of the input. Q在那里标记输入的结束。 I am using fileIn.hasNextInt() to read the input and check to see if it is an integer.
我正在使用fileIn.hasNextInt()读取输入并检查是否为整数。
The problem I am having with my logic is it is only cycling through the ArrayList and returning the last index of the ArrayList and not the index of the second largest value. 我的逻辑存在的问题是,它仅循环遍历ArrayList并返回ArrayList的最后一个索引,而不是第二大值的索引。
Here is my code: 这是我的代码:
public static int secondMaxIndex(ArrayList<Integer> intArray){
int largest = intArray.get(0);
int largest2 = intArray.get(0);
int maxIndex2 = 0;
for( int i = 0; i <= intArray.size() - 1; i++){
if( largest < intArray.get(i) ){
largest = intArray.get(i);
}
}
for( int j = 0; j <= intArray.size() - 1; j++){
if( intArray.get(j) < largest ){
maxIndex2 = j;
}
}
return maxIndex2;
}
You are inventing a wheel. 您正在发明轮子。
ArrayList<Integer> intArray
contains Integers
by contract, no need to verify its elements. ArrayList<Integer> intArray
通过合同包含Integers
,无需验证其元素。 Just use natural sorting and pick second item from the end: 只需使用自然排序,然后从末尾选择第二个项目:
intArray.sort(Integer::compare);
return intArray.get(intArray.size - 2);
if ( intArray.get(j) < largest ) {
maxIndex2 = j;
}
Here is your problem. 这是你的问题。 Think about it, this code won't just return the second largest, it will return a number that is smaller than the largest number.
考虑一下,此代码不仅会返回第二大数字,还会返回小于最大数字的数字。
public static int secondMaxIndex(ArrayList<Integer> intArray)
{
int largest = intArray.get(0);
Integer largest2 = null;
int maxIndex = 0;
int maxIndex2 = 0;
for( int i = 0; i < intArray.size() ; i++)
{
if( largest < intArray.get(i) )
{
largest2 = largest;
maxIndex2 = maxIndex;
largest = intArray.get(i);
maxIndex = i;
}
else if(largest2 == null || intArray.get(i) > largest2)
{
largest2 = intArray.get(i);
maxIndex2 = i;
}
}
return maxIndex2;
}
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