tags: - cocubes - coding - practice
Coding Practice Problems
These are original, high-yield problems selected to cover commonly reported CoCubes-style skills. Time yourself.
Problem 1 ā Unit digit of a power
Given non-negative integers x and y, print the unit digit of x raised to y. Do not compute the full power when y is large.
Target: O(1) or O(log y), depending on method.
Problem 2 ā Card total
Given n integer card values, print their total and the count of positive cards.
Target: O(n), O(1) extra space.
Problem 3 ā First unique character
Given a lowercase string, print the first character that occurs exactly once. Print -1 if none exists.
Target: O(n), frequency map.
Problem 4 ā Pair with target sum
Given an array and target T, determine whether two distinct positions have values that sum to T.
Target: O(n) average with hash set/map.
Problem 5 ā Valid palindrome
Given a string containing letters and digits, ignore case and non-alphanumeric characters. Determine whether it is a palindrome.
Target: O(n), two pointers.
Problem 6 ā Balanced brackets
Given a string of parentheses, square brackets and braces, determine whether it is balanced.
Target: O(n), stack.
Problem 7 ā Second largest distinct value
Given n integers, print the second largest distinct value, or -1 if it does not exist.
Target: O(n), O(1) extra space.
Problem 8 ā Longest equal-half digit substring
Given a digit string, find the maximum even length such that the sum of the first half equals the sum of the second half.
Target: try O(nĀ²) after understanding constraints; prefix sums can improve sum checks.
Problem 9 ā Count subarrays with sum K
Given integer array and K, count contiguous subarrays with sum K.
Target: O(n) average with prefix-sum frequency map.
Problem 10 ā Grid shortest path
Given a grid with open cells and blocked cells, find shortest four-direction path length from start to target, or -1.
Target: O(rows Ć columns), BFS.
Solutions and methods: [[05_Coding/Coding_Solutions|Coding solutions]].