Count Occurs Once

L2 Easy Arrays & Hashing

Concept

When you need to know how many times each value appears, a Dictionary counting tally into value frequencies is the standard move.

Return how many distinct values in nums appear exactly once. Values that repeat do not count at all.

Examples

▸ nums = [1, 2, 2, 3, 3, 3]

→ 1

▸ nums = []

→ 0

▸ nums = [5]

→ 1

Progressive Hints

Hint 1 · Nudge

You need to know how often each value appears before you can decide which ones count.

Hint 2 · Plan

First tally every number into a frequency map. Then count how many entries have a tally of exactly 1 and return that.

Hint 3 · Approach

counts = a map from value to tally. For each n: counts[n] = counts[n] + 1. Then count the keys whose tally equals 1. Return that count.

Output

// Run your code to see the output here.