| 1 | /**
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| 2 | * For a sorted input, counting the number of unique values
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| 3 | * is possible in constant time and constant memory. This is
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| 4 | * a simple implementation of the algorithm.
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| 5 | *
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| 6 | * Values are compared with `===`, so objects and non-primitive objects
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| 7 | * are not handled in any special way.
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| 8 | *
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| 9 | * @param {Array<*>} x an array of any kind of value
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| 10 | * @returns {number} count of unique values
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| 11 | * @example
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| 12 | * uniqueCountSorted([1, 2, 3]); // => 3
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| 13 | * uniqueCountSorted([1, 1, 1]); // => 1
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| 14 | */
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| 15 | function uniqueCountSorted(x) {
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| 16 | let uniqueValueCount = 0,
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| 17 | lastSeenValue;
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| 18 | for (let i = 0; i < x.length; i++) {
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| 19 | if (i === 0 || x[i] !== lastSeenValue) {
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| 20 | lastSeenValue = x[i];
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| 21 | uniqueValueCount++;
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| 22 | }
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| 23 | }
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| 24 | return uniqueValueCount;
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| 25 | }
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| 26 |
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| 27 | export default uniqueCountSorted;
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