使用ES6数组方法找出小行星发现次数最多的年份

Issues with the Original Code #

The provided code has three critical problems:

• Syntax Error: The parentheses around (acc, val) are incorrectly placed before the arrow function, leading to invalid JavaScript syntax.
• Incomplete Logic: The function only generates a count of occurrences per year but does not extract the year with the highest count.
• Accumulator Return: The arrow function does not return the accumulator object, breaking the reduce operation (each iteration would return the count value instead of updating the accumulator).

Corrected Code #

function getGreatestDiscoveryYear(data) {
    // Step 1: Count how many asteroids were discovered each year
    const yearCounts = data.asteroids.reduce((acc, asteroid) => {
        const year = asteroid.discoveryYear;
        acc[year] = (acc[year] || 0) + 1;
        return acc;
    }, {});

    // Step 2: Find the year with the highest discovery count
    const [mostFrequentYear] = Object.entries(yearCounts).reduce((maxEntry, currentEntry) => {
        return currentEntry[1] > maxEntry[1] ? currentEntry : maxEntry;
    });

    return Number(mostFrequentYear);
}

How It Works #

1. Counting Years:

   • We use reduce to iterate over the asteroids array, building an object where keys are discovery years and values are the number of asteroids discovered that year.
   • For each asteroid, we increment the count for its discovery year (initializing to 0 if the year isn't already in the accumulator).
   • We explicitly return the accumulator object after each update to ensure reduce works correctly.

2. Finding the Most Frequent Year:

   • Object.entries(yearCounts) converts the count object into an array of [year, count] pairs.
   • Another reduce call compares each pair to find the one with the highest count.
   • We convert the year string back to a number before returning it (since Object.entries returns keys as strings).

Test Result #

When run with the provided asteroid data, this function returns 1847—the year with the most asteroid discoveries (3 asteroids: 6 Hebe, 7 Iris, 8 Flora).

内容的提问来源于stack exchange，提问作者OldsoulPhil