2012 Lanqiao Cup Java Vocational Problems: Analysis and Techniques

This article reviews the 2012 Lanqiao Cup Java vocational-group problems and the programming techniques commonly required to solve them.

Read the problem as a specification

Identify the exact input range, required output format, edge cases, and whether the task asks for a value, count, arrangement, or proof. Small input bounds may permit enumeration; larger bounds usually require dynamic programming, graph algorithms, number theory, or an optimized data structure.

Build the simplest correct model

Typical contest patterns include:

• nested loops and simulation;
• string and digit processing;
• recursion, permutations, and backtracking;
• greatest common divisor and modular arithmetic;
• sorting, binary search, and prefix sums;
• dynamic programming for repeated subproblems.

Before coding, estimate time and memory complexity. An O(n²) solution may be acceptable for a few thousand elements but not for millions.

Java implementation details

Use buffered input and output when the data set is large. Prefer long when intermediate arithmetic can exceed the int range. Keep indexing conventions consistent and test minimum, maximum, duplicate, empty, and boundary cases.

BufferedReader reader = new BufferedReader(
    new InputStreamReader(System.in));
StringBuilder output = new StringBuilder();

Contest workflow

First implement a clear baseline solution and verify it against hand-calculated examples. Optimize only after identifying the actual bottleneck. During the contest, preserve working versions, avoid unnecessary framework code, and compare the final output exactly with the required format.

The original article contains the individual problem attempts and code. Their lasting value is the reasoning process: translate the statement into a precise model, select an algorithm supported by the constraints, and validate every boundary condition.