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78 lines
1.6 KiB
Markdown
78 lines
1.6 KiB
Markdown
---
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id: 68b7cadffed0e75a517da673
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title: "Challenge 52: Binary to Decimal"
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challengeType: 29
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dashedName: challenge-52
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---
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# --description--
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Given a string representing a binary number, return its decimal equivalent as a number.
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A binary number uses only the digits `0` and `1` to represent any number. To convert binary to decimal, multiply each digit by a power of `2` and add them together. Start by multiplying the rightmost digit by `2^0`, the next digit to the left by `2^1`, and so on. Once all digits have been multiplied by a power of `2`, add the result together.
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For example, the binary number `101` equals `5` in decimal because:
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```mathml
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1 * 2^2 + 0 * 2^1 + 1 * 2^0 = 4 + 0 + 1 = 5
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```
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# --hints--
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`to_decimal("101")` should return `5`.
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```js
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({test: () => { runPython(`
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from unittest import TestCase
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TestCase().assertEqual(to_decimal("101"), 5)`)
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}})
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```
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`to_decimal("1010")` should return `10`.
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```js
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({test: () => { runPython(`
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from unittest import TestCase
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TestCase().assertEqual(to_decimal("1010"), 10)`)
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}})
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```
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`to_decimal("10010")` should return `18`.
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```js
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({test: () => { runPython(`
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from unittest import TestCase
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TestCase().assertEqual(to_decimal("10010"), 18)`)
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}})
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```
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`to_decimal("1010101")` should return `85`.
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```js
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({test: () => { runPython(`
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from unittest import TestCase
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TestCase().assertEqual(to_decimal("1010101"), 85)`)
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}})
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```
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# --seed--
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## --seed-contents--
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```py
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def to_decimal(binary):
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return binary
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```
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# --solutions--
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```py
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def to_decimal(binary):
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decimal = 0
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for i, bit_char in enumerate(reversed(binary)):
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bit = int(bit_char)
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decimal += bit * (2 ** i)
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return decimal
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```
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