SDE - 1

You are given a string ‘S’ of length ‘N’. The string ‘S’ consists of only two characters ‘X’ and ‘Y’. In one operation, you can select two indices ‘i’ and ‘j’, and flip each character of the substring from ‘i’ to ‘j’. Flip the characters means changing the character ‘X’ to ‘Y’ and the character ‘Y’ to ‘X’.

You need to perform exactly one operation. Find the maximum number of ‘X’s in the string ‘S’ that you can get after performing the operation.

Example:

Input: ‘N’ = 4,  ‘S’ = “XYYX”

Output: 4.

Select ‘i’ = 1 and ‘j’ = 2. Flip all the characters of the substring from 1 to 2, and we get ‘S’ = ‘XXXX’. Hence, the number of ‘X’s is 4.

A virus travels on a positive number line with a range from 0 to ‘R’ in which it can travel only in the left or right direction. You are given a string ‘PATH’ representing the sequence of moves a virus can move. Your task is to find the number of distinct subsequences of those moves that lead from a given point ‘X’ to point ‘Y’ on the number line. If a virus is present at position ‘P’, then moving in the ‘l’ direction will take it to the ‘P’ - 1 position, whereas moving in the ‘r’ direction will take it to the ‘P’ + 1 position.

Note:

Subsequences are created by deleting 0 or more characters from a sequence without changing the order.

Example:

Let ‘PATH’ be: "rrr"
Let ‘X’ = 1, ‘Y’ = 2, and ‘R’ = 10
Paths are ["r", "r", "r"]. As we have to choose distinct subsequences, so the result is 1.

Given a binary tree, convert this binary tree into its mirror tree.

A binary tree is a tree in which each parent node has at most two children.

Mirror of a Tree: Mirror of a Binary Tree T is another Binary Tree M(T) with left and right children of all non-leaf nodes interchanged.

Note:

1. Make in-place changes, that is, modify the nodes given a binary tree to get the required mirror tree.

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