Software Engineer

1. Create a count array to store the frequency of each character in the given string.
2. Traverse the string again and check whether the frequency of that character is 0 or not.
3. If not 0, then print the character along with its frequency and update its frequency to 0 in the hash table. This is done so that the same character is not printed again.
Time Complexity: O(n), where n is the number of characters in the string. 
Auxiliary Space: O(1), as there are only lowercase letters.

Method hiding can be defined as, "if a subclass defines a static method with the same signature as a static method in the super class, in such a case, the method in the subclass hides the one in the superclass." The mechanism is known as method hiding. It happens because static methods are resolved at compile time.

We have multiple ways of passing data among components. We can pass data from parent to child, from child to parent, and between siblings.
Passing data from Parent to Child:
For passing data from parent to child component, we use props. Props data is sent by the parent component and cannot be changed by the child component as they are read-only.

Passing data from Child to Parent Component:
For passing the data from the child component to the parent component, we have to create a callback function in the parent component and then pass the callback function to the child component as a prop. This callback function will retrieve the data from the child component. The child component calls the parent callback function using props and passes the data to the parent component.

Passing data between Siblings:
For passing data among siblings, there are multiple methods:
Combination of the above two methods (callback and use of props).
Using Redux.
ContextAPI

Each component in React has a lifecycle which you can monitor and manipulate during its three main phases.
The three phases are: Mounting, Updating, and Unmounting.

1. Mounting means putting elements into the DOM.
React has four built-in methods that gets called, in this order, when mounting a component:
constructor()
getDerivedStateFromProps()
render()
componentDidMount()

2. The next phase in the lifecycle is when a component is updated.
A component is updated whenever there is a change in the component's state or props.
React has five built-in methods that gets called, in this order, when a component is updated:
getDerivedStateFromProps()
shouldComponentUpdate()
render()
getSnapshotBeforeUpdate()
componentDidUpdate()

3.The next phase in the lifecycle is when a component is removed from the DOM, or unmounting as React likes to call it.
React has only one built-in method that gets called when a component is unmounted:
componentWillUnmount()

When a component’s props or state change, React decides whether an actual DOM update is necessary by comparing the newly returned element with the previously rendered one. When they are not equal, React will update the DOM.