Range Bit Count
Description
You are given two numbers a and b where 0 ≤ a ≤ b. Imagine you construct an array of all the integers from a to b inclusive. You need to count the number of 1s in the binary representations of all the numbers in the array.
Example
For a = 2 and b = 7, the output should be
rangeBitCount(a, b) = 11.
Given a = 2 and b = 7 the array is: [2, 3, 4, 5, 6, 7]. Converting the numbers to binary, we get [10, 11, 100, 101, 110, 111], which contains 1 + 2 + 1 + 2 + 2 + 3 = 11 1s.
Input/Output
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[execution time limit] 4 seconds (js)
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[input] integer a
Guaranteed constraints:
0 \leq a \leq b. -
[input] integer b
Guaranteed constraints:
a \leq b \leq 10. -
[output] integer
[JavaScript (ES6)] Syntax Tips
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// Prints help message to the console
// Returns a string
function helloWorld(name) {
console.log("This prints to the console when you Run Tests");
return "Hello, " + name;
}
Solution
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function rangeBitCount(a, b) {
var ret = 0;
for (var i = a; i <= b; i++) {
ret += [0, 1, 2, 3].reduce((acc, d) => acc + ((i & 1 << d) >> d), 0);
}
return ret;
}