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1356-Sort-Integers-by-The-Number-of-1-Bits.cpp
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1356-Sort-Integers-by-The-Number-of-1-Bits.cpp
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// Author : Vicen-te
// Date : 10/30/2023 (MM-DD-YYYY)
/**
*
* Description:
* You are given an integer array arr. Sort the integers in the array in ascending order by
* the number of 1's in their binary representation and in case of two or more integers have
* the same number of 1's you have to sort them in ascending order.
*
* Return the array after sorting it.
*
* Ex1.
* Input: arr = [0,1,2,3,4,5,6,7,8]
* Output: [0,1,2,4,8,3,5,6,7]
* Explanation:
* [0] is the only integer with 0 bits.
* [1,2,4,8] all have 1 bit.
* [3,5,6] have 2 bits.
* [7] has 3 bits.
* The sorted array by bits is [0,1,2,4,8,3,5,6,7]
*
* Ex2.
* Input: arr = [1024,512,256,128,64,32,16,8,4,2,1]
* Output: [1,2,4,8,16,32,64,128,256,512,1024]
* Explanation:
* All integers have 1 bit in the binary representation,
* you should just sort them in ascending order.
*
* Algorithm:
* This C++ solution uses the std::sort method to sort an array of integers based
* on the count of set bits (1s) in their binary representations.
*
* The process involves the following steps:
*
* 1. Initialize two variables, 'ca' and 'cb', to count the number of set bits
* in integers 'a' and 'b.'
*
* 2. Use bitwise operators to calculate the set bit count.
*
* 3. If the set bit counts are equal, compare numerically; otherwise, sort by the
* set bit count in ascending order.
*
* Time: O(NlognN)
* Space: O(N)
*/
// Built-in Functions
class Solution {
public:
static bool compare (int& a, int& b)
{
int ca = 0, cb = 0; //< Another option: __builtin_popcount
for(int i = 0; i < 14; ++i){ // limit == 14 bits == 10^4
if(a&(1<<i)){
++ca;
}
}
for(int j = 0; j < 14; ++j){
if(b&(1<<j)){
++cb;
}
}
return (cb == ca) ? a < b : ca < cb;
}
vector<int> sortByBits(vector<int>& arr) {
sort(arr.begin(), arr.end(), compare);
return arr;
}
};
// Brian Kerninghan's Algorithm
class Solution {
public:
static int bits(int num) {
int cnt = 0;
while (num){
num &= (num - 1);
++cnt;
}
return cnt;
}
static bool compare(int& a, int& b) {
int ca = bits(a);
int cb = bits(b);
return (cb == ca) ? a < b : ca < cb;
}
vector<int> sortByBits(vector<int>& arr) {
sort(arr.begin(), arr.end(), compare);
return arr;
}
};