给定一个正整数N ,任务是计算从1到N的所有数字的二进制表示中设置位的总数。
例子:
Input: N = 3
Output: 4
setBits(1) + setBits(2) + setBits(3) = 1 + 1 + 2 = 4
Input: N = 6
Output: 9
处理方法:此问题的解决方案已在本文的Set 1 和Set 2 中发布。在这里,讨论了基于动态规划的方法。
- 基本情况: 0 中的设置位数为 0。
- 对于任何数字 n: n 和 n>>1 除了最右边的位外,具有相同的设置位。
示例:n = 11 ( 101 1), n >> 1 = 5 ( 101 )… 11 和 5 中的相同位用粗体标记。所以假设我们已经知道设置位数为 5,我们只需要注意 11 的最右边的位是 1。 setBit(11) = setBit(5) + 1 = 2 + 1 = 3
最右边的位是奇数为 1,偶数为 0。
循环关系: setBit(n) = setBit(n>>1) + (n & 1) and setBit(0) = 0
我们可以使用自底向上的动态规划方法来解决这个问题。
下面是上述方法的实现:
C++
// C++ implementation of the approach
#include
using namespace std;
// Function to return the count of
// set bits in all the integers
// from the range [1, n]
int countSetBits(int n)
{
// To store the required count
// of the set bits
int cnt = 0;
// To store the count of set
// bits in every integer
vector setBits(n + 1);
// 0 has no set bit
setBits[0] = 0;
for (int i = 1; i <= n; i++) {
setBits[i] = setBits[i >> 1] + (i & 1);
}
// Sum all the set bits
for (int i = 0; i <= n; i++) {
cnt = cnt + setBits[i];
}
return cnt;
}
// Driver code
int main()
{
int n = 6;
cout << countSetBits(n);
return 0;
}
Java
// Java implementation of the approach
import java.util.*;
class GFG
{
// Function to return the count of
// set bits in all the integers
// from the range [1, n]
static int countSetBits(int n)
{
// To store the required count
// of the set bits
int cnt = 0;
// To store the count of set
// bits in every integer
int []setBits = new int[n + 1];
// 0 has no set bit
setBits[0] = 0;
// For the rest of the elements
for (int i = 1; i <= n; i++) {
setBits[i] = setBits[i >> 1] + (i & 1);
}
// Sum all the set bits
for (int i = 0; i <= n; i++)
{
cnt = cnt + setBits[i];
}
return cnt;
}
// Driver code
public static void main(String[] args)
{
int n = 6;
System.out.println(countSetBits(n));
}
}
// This code is contributed by Princi Singh
Python3
# Python3 implementation of the approach
# Function to return the count of
# set bits in all the integers
# from the range [1, n]
def countSetBits(n):
# To store the required count
# of the set bits
cnt = 0
# To store the count of set
# bits in every integer
setBits = [0 for x in range(n + 1)]
# 0 has no set bit
setBits[0] = 0
# For the rest of the elements
for i in range(1, n + 1):
setBits[i] = setBits[i // 2] + (i & 1)
# Sum all the set bits
for i in range(0, n + 1):
cnt = cnt + setBits[i]
return cnt
# Driver code
n = 6
print(countSetBits(n))
# This code is contributed by Sanjit Prasad
C#
// C# implementation of the approach
using System;
class GFG
{
// Function to return the count of
// set bits in all the integers
// from the range [1, n]
static int countSetBits(int n)
{
// To store the required count
// of the set bits
int cnt = 0;
// To store the count of set
// bits in every integer
int []setBits = new int[n + 1];
// 0 has no set bit
setBits[0] = 0;
// 1 has a single set bit
setBits[1] = 1;
// For the rest of the elements
for (int i = 2; i <= n; i++)
{
// If current element i is even then
// it has set bits equal to the count
// of the set bits in i / 2
if (i % 2 == 0)
{
setBits[i] = setBits[i / 2];
}
// Else it has set bits equal to one
// more than the previous element
else
{
setBits[i] = setBits[i - 1] + 1;
}
}
// Sum all the set bits
for (int i = 0; i <= n; i++)
{
cnt = cnt + setBits[i];
}
return cnt;
}
// Driver code
static public void Main ()
{
int n = 6;
Console.WriteLine(countSetBits(n));
}
}
// This code is contributed by AnkitRai01
Javascript
C++
// C++ implementation of the approach
#include
using namespace std;
// Function to return the count of
// set bits in all the integers
// from the range [1, n]
int countSetBits(int n)
{
// To store the required count
// of the set bits
int cnt = 0;
// Calculate set bits in each number using
// __builtin_popcount() and Sum all the set bits
for (int i = 1; i <= n; i++) {
cnt = cnt + __builtin_popcount(i);
}
return cnt;
}
// Driver code
int main()
{
int n = 6;
cout << countSetBits(n);
return 0;
}
// This article is contributed by Abhishek
输出:
9
另一个简单易懂的解决方案:
一个简单易于实现和理解的解决方案是不使用位操作。解决方案是使用 __builtin_popcount() 直接计算设置位。解决方案在代码中使用注释进行了解释。
C++
// C++ implementation of the approach
#include
using namespace std;
// Function to return the count of
// set bits in all the integers
// from the range [1, n]
int countSetBits(int n)
{
// To store the required count
// of the set bits
int cnt = 0;
// Calculate set bits in each number using
// __builtin_popcount() and Sum all the set bits
for (int i = 1; i <= n; i++) {
cnt = cnt + __builtin_popcount(i);
}
return cnt;
}
// Driver code
int main()
{
int n = 6;
cout << countSetBits(n);
return 0;
}
// This article is contributed by Abhishek
输出
9
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