Collection<T>.IndexOf(T) method is used to search for the specified object and returns the zero-based index of the first occurrence within the entire Collection<T>.
public int IndexOf (T item);
Here, item is the object to locate in the List<T>. The value can be null for reference types.
Return Value: This method returns the zero-based index of the first occurrence of item within the entire Collection<T>, if found, otherwise, -1.
Below given are some examples to understand the implementation in a better way:
A B C D D E Index : 3
2 3 4 5 Index : -1
- The Collection<T> is searched forward starting at the first element and ending at the last element.
- This method determines equality using the default equality comparer EqualityComparer<T>.Default for T, the type of values in the list.
- This method performs a linear search. Therefore, this method is an O(n) operation, where n is Count.