32 lines
771 B
TypeScript
32 lines
771 B
TypeScript
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// n! means n × (n − 1) × ... × 3 × 2 × 1
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// For example, 10! = 10 × 9 × ... × 3 × 2 × 1 = 3628800,and the sum of the digits in the number 10! is 3 + 6 + 2 + 8 + 8 + 0 + 0 = 27.
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// Find the sum of the digits in the number 100!
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export = {};
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/**
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* Calculate n! as a BigInt
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*/
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const factorial = (n: number) => {
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if (n < 0) return BigInt(-1);
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else if (n === 0) return BigInt(1);
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else return BigInt(BigInt(n) * factorial(n - 1));
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};
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/**
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* Find the sum of the digits in a number
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*/
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const sumOfDigits = (n: number) => {
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let sum = 0;
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n.toString()
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.split('')
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.map(d => parseInt(d))
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.forEach(digit => (sum += digit));
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return sum;
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};
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// Output
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const digitSum = sumOfDigits(factorial(100));
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console.log(digitSum);
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