thefourtheye.in

Celebrates the author's Python solution being featured in SPOJ's Top 20 for The Double Helix problem. A competitive programming milestone.

Project Euler Problem 15 - Lattice paths. Count routes through an NxN grid moving only right and down using dynamic programming. Solution builds from bottom-right corner.

Project Euler Problem 14 - Longest Collatz sequence. Demonstrates memoization to dramatically speed up computing chain lengths for the Collatz conjecture.

Project Euler Problem 5 - Smallest Multiple. Finds the smallest number divisible by all numbers 1-20. Compares brute force approach to optimized LCM-based solution using GCD.

Project Euler problems 18 and 67 - Maximum path sum. Classic DP problem: find the maximum sum from top to bottom of a triangular number pyramid by propagating maximums upward.

Google Code Jam 2013 Round 1B Osmos problem solution. Uses greedy algorithm with the ability to grow (add to your size) or remove enemies to find minimum changes needed.

Shows how to redirect stdin and stdout in Python to work with files, similar to C's freopen(). Enables automating interactive programs in competitive programming.

SPOJ ACODE - AlphaCode. Counts possible decodings of a numeric string where 1=A, 2=B, ..., 26=Z using dynamic programming. Handles single and double digit interpretations.

Timus problem 1018 - Binary Apple Tree. Uses dynamic programming to determine which branches to keep to maximize apples collected when only Q branches can be retained.

UVa 11259 - Coin Changing Again. Uses top-down dynamic programming with state encoding to find all possible ways to make change with limited coin counts. Includes solution with memoization.

A variant of the change making problem that counts the number of distinct ways to make change for a given amount using dynamic programming with coin denominations.

Classic dynamic programming problem to find the minimum number of coins needed to make a given change. Uses a bottom-up approach with sorted denominations to compute optimal solution.

A classic SPOJ problem requiring string manipulation to find the smallest palindrome greater than a given number with up to 1 million digits. Explains the algorithm approach using string reflection and handling edge cases like all-9s numbers.

SPOJ problem ONP - Transform algebraic expressions with brackets into Reverse Polish Notation (RPN). Uses a stack-based algorithm to convert infix expressions to postfix for easier evaluation.

Covers multiple algorithms for testing primality - from basic O(n) trial division to optimized approaches checking only up to square root, and skipping even numbers after 2.