2734. Lexicographically Smallest String After Substring Operation

You are given a string s consisting of only lowercase English letters. In one operation, you can do the following:

• Select any non-empty substring of s, possibly the entire string, then replace each one of its characters with the previous character of the English alphabet. For example, ‘b’ is converted to ‘a’, and ‘a’ is converted to ‘z’.

Return the lexicographically smallest string you can obtain after performing the above operation exactly once.

A substring is a contiguous sequence of characters in a string.

A string x is lexicographically smaller than a string y of the same length if x[i] comes before y[i] in alphabetic order for the first position i such that x[i] != y[i].

2733. Neither Minimum nor Maximum

Given an integer array nums containing distinct positive integers, find and return any number from the array that is neither the minimum nor the maximum value in the array, or -1 if there is no such number.

Return the selected integer.

Codeforces Round 145 (Div. 2, ACM-ICPC Rules) F. Fence

Codeforces Round 148 (Div. 1) B. Boring Partition

Codeforces Round 149 (Div. 2) C. King’s Path

CROC-MBTU 2012, Elimination Round (ACM-ICPC) H. Queries for Number of Palindromes

Codeforces Round 153 (Div. 1) B. Playing with Permutations

2732. Find a Good Subset of the Matrix

You are given a 0-indexed m x n binary matrix grid.

Let us call a non-empty subset of rows good if the sum of each column of the subset is at most half of the length of the subset.

More formally, if the length of the chosen subset of rows is k, then the sum of each column should be at most floor(k / 2).

Return an integer array that contains row indices of a good subset sorted in ascending order.

If there are multiple good subsets, you can return any of them. If there are no good subsets, return an empty array.

A subset of rows of the matrix grid is any matrix that can be obtained by deleting some (possibly none or all) rows from grid.

2731. Movement of Robots

Some robots are standing on an infinite number line with their initial coordinates given by a 0-indexed integer array nums and will start moving once given the command to move. The robots will move a unit distance each second.

You are given a string s denoting the direction in which robots will move on command. 'L' means the robot will move towards the left side or negative side of the number line, whereas 'R' means the robot will move towards the right side or positive side of the number line.

If two robots collide, they will start moving in opposite directions.

Return the sum of distances between all the pairs of robots d seconds after the command. Since the sum can be very large, return it modulo 109 + 7.

Note:

• For two robots at the index i and j, pair (i,j) and pair (j,i) are considered the same pair.
• When robots collide, they instantly change their directions without wasting any time.
• Collision happens when two robots share the same place in a moment.
  • For example, if a robot is positioned in 0 going to the right and another is positioned in 2 going to the left, the next second they’ll be both in 1 and they will change direction and the next second the first one will be in 0, heading left, and another will be in 2, heading right.
  • For example, if a robot is positioned in 0 going to the right and another is positioned in 1 going to the left, the next second the first one will be in 0, heading left, and another will be in 1, heading right.

2730. Find the Longest Semi-Repetitive Substring

You are given a 0-indexed string s that consists of digits from 0 to 9.

A string t is called a semi-repetitive if there is at most one consecutive pair of the same digits inside t.

Return the length of the longest semi-repetitive substring inside s.

A substring is a contiguous non-empty sequence of characters within a string.