Test clarity issue: Conflicting requirements for getIntervalArray implementation

[samolevich]

Problem Description

The current test implementation creates confusion about expectations for the getIntervalArray function:

Current Issues:

1. Unclear Test Failure Message: When the test fails, it's not immediately obvious that Array.from() is expected unless you examine the test code directly
2. Misleading Test Description: The test is named "optimal implementation" but enforces a specific method rather than actual optimal performance
3. Contradictory Requirements: The description suggests optimal algorithm, but the code checks for Array.from() usage specifically

Performance Analysis

Based on performance testing, here are implementations from most optimal to least optimal:

function testWithConsoleTime() {
    console.log('🚀 PERFORMANCE TEST: getIntervalArray implementations');
    console.log('Range: 1..1000, Iterations: 1000');
    console.log('====================================================');
    
    // 🏆 BEST - for loop with push (most optimal)
    function bestForPush(s, e) {
        const arr = [];
        for (let i = s; i <= e; i++) arr.push(i);
        return arr;
    }
    
    // 🥈 GOOD - Array.from (clean syntax, good performance)
    function goodArrayFrom(s, e) {
        return Array.from({ length: e - s + 1 }, (_, i) => s + i);
    }
    
    // 🥉 ACCEPTABLE - Array.fill + map
    function acceptableFillMap(s, e) {
        return Array(e - s + 1).fill().map((_, i) => s + i);
    }
    
    // ⚠️ SUBOPTIMAL - Single spread (not in loop)
    function suboptimalSpread(s, e) {
        return [...Array(e - s + 1)].map((_, i) => s + i);
    }
    
    // ❌ BAD - Spread in loop (creates new array each iteration)
    function badSpreadInLoop(s, e) {
        let arr = [];
        for (let i = s; i <= e; i++) {
            arr = [...arr, i];
        }
        return arr;
    }
    
    // ❌ VERY BAD - Concat in loop (worst performance)
    function veryBadConcatInLoop(s, e) {
        let arr = [];
        for (let i = s; i <= e; i++) {
            arr = arr.concat(i);
        }
        return arr;
    }
    
    // ❌ TERRIBLE - Recursion with spread (stack and performance issues)
    function terribleRecursionSpread(s, e, arr = []) {
        return s > e ? arr : terribleRecursionSpread(s + 1, e, [...arr, s]);
    }
    
    // ❌ WORST - Recursion with concat (maximum inefficiency)
    function worstRecursionConcat(s, e, arr = []) {
        return s > e ? arr : worstRecursionConcat(s + 1, e, arr.concat(s));
    }

    const testRange = [1, 1000];
    const iterations = 1000;

    // 🏆 BEST PERFORMANCE
    console.log('\n✅ OPTIMAL SOLUTIONS:');
    console.time('🏆 for + push');
    for (let i = 0; i < iterations; i++) bestForPush(...testRange);
    console.timeEnd('🏆 for + push');
    
    console.time('🥈 Array.from');
    for (let i = 0; i < iterations; i++) goodArrayFrom(...testRange);
    console.timeEnd('🥈 Array.from');
    
    console.time('🥉 fill + map');
    for (let i = 0; i < iterations; i++) acceptableFillMap(...testRange);
    console.timeEnd('🥉 fill + map');
    
    // ⚠️ SUBOPTIMAL
    console.log('\n⚠️  SUBOPTIMAL SOLUTIONS:');
    console.time('🔸 spread + map');
    for (let i = 0; i < iterations; i++) suboptimalSpread(...testRange);
    console.timeEnd('🔸 spread + map');
    
    // ❌ INEFFICIENT
    console.log('\n❌ INEFFICIENT SOLUTIONS:');
    console.time('🔻 spread in loop');
    for (let i = 0; i < iterations; i++) badSpreadInLoop(...testRange);
    console.timeEnd('🔻 spread in loop');
    
    console.time('🔻 concat in loop');
    for (let i = 0; i < iterations; i++) veryBadConcatInLoop(...testRange);
    console.timeEnd('🔻 concat in loop');
    
    // ❌ VERY INEFFICIENT (reduced iterations for stability)
    console.log('\n❌ VERY INEFFICIENT (100 iterations):');
    console.time('💀 recursion + spread');
    for (let i = 0; i < 100; i++) terribleRecursionSpread(...testRange);
    console.timeEnd('💀 recursion + spread');
    
    console.time('💀 recursion + concat');
    for (let i = 0; i < 100; i++) worstRecursionConcat(...testRange);
    console.timeEnd('💀 recursion + concat');

    // Performance comparison summary
    console.log('\n📊 PERFORMANCE SUMMARY:');
    console.log('🏆 Best: for + push (fastest, minimal memory)');
    console.log('🥈 Good: Array.from (clean, functional style)');
    console.log('❌ Avoid: concat/spread in loops (O(n²) complexity)');
    console.log('💀 Never: recursion with array copying (stack overflow risk)');
}

// Run the performance test
testWithConsoleTime();

// Additional test with smaller range to show pattern clearly
function testSmallRange() {
    console.log('\n\n🔍 DETAILED TEST: Small range (1..100)');
    console.log('======================================');
    
    function forPush(s, e) { const a = []; for (let i = s; i <= e; i++) a.push(i); return a; }
    function arrayFrom(s, e) { return Array.from({ length: e - s + 1 }, (_, i) => s + i); }
    function concatLoop(s, e) { let a = []; for (let i = s; i <= e; i++) a = a.concat(i); return a; }
    function spreadLoop(s, e) { let a = []; for (let i = s; i <= e; i++) a = [...a, i]; return a; }

    const smallRange = [1, 100];
    const smallIterations = 5000;

    console.time('for + push (small)');
    for (let i = 0; i < smallIterations; i++) forPush(...smallRange);
    console.timeEnd('for + push (small)');
    
    console.time('Array.from (small)');
    for (let i = 0; i < smallIterations; i++) arrayFrom(...smallRange);
    console.timeEnd('Array.from (small)');
    
    console.time('concat in loop (small)');
    for (let i = 0; i < smallIterations; i++) concatLoop(...smallRange);
    console.timeEnd('concat in loop (small)');
    
    console.time('spread in loop (small)');
    for (let i = 0; i < smallIterations; i++) spreadLoop(...smallRange);
    console.timeEnd('spread in loop (small)');
}

testSmallRange();

This test structure clearly shows:

🏆 Best performance: for + push (optimal for this use case)

🥈 Good performance: Array.from (clean but slightly slower)

🥉 Acceptable: Other efficient methods

❌ Bad: Methods with performance issues

💀 Worst: Methods with both performance and stability issues

The tests demonstrate why:

for + push should be considered the most optimal

Array.from is a good alternative but not "the most optimal"

concat and spread in loops should be restricted for performance reasons

Proposed Solutions

it.optional('implementation using Array.from', function test() {
  const fnStr = tasks.getIntervalArray.toString();
  if (!fnStr.includes('return')) {
    this.skip();
  }
  assert.equal(
    fnStr.includes('from'),
    true,
    'This task is designed specifically to practice Array.from() method. Please implement the solution using Array.from() as described in the documentation: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/from'
  );
});

or

it.optional('optimal implementation of getIntervalArray', function test() {
  const fnStr = tasks.getIntervalArray.toString();
  if (!fnStr.includes('return')) {
    this.skip();
  }
  
  // Restrict concat usage which always indicates poor performance
  assert.equal(
    fnStr.includes('concat'),
    false,
    'Avoid using concat for array building in loops as it creates performance issues. Consider using push() or Array.from() for better efficiency.'
  );
});