给定两个正整数L 和 R ,任务是计算范围[L, R] 中质因数仅为 2 和 3的元素。
例子:
Input: L = 1, R = 10
Output: 6
Explanation:
2 = 2
3 = 3
4 = 2 * 2
6 = 2 * 3
8 = 2 * 2 * 2
9 = 3 * 3
Input: L = 100, R = 200
Output: 5
对于更简单的方法,请参阅从质因数仅为 2 和 3 的范围中计算数字。
方法:
要以优化的方式解决问题,请按照以下步骤操作:
- 将所有小于或等于 R的 2 的幂存储在数组power2[] 中。
- 类似地,将所有小于或等于 R的 3 的幂存储在另一个数组power3[] 中。
- 初始化第三个数组power23[]并存储power2[]的每个元素与power3[] 的每个元素小于或等于R的成对乘积。
- 现在对于任何范围[L, R] ,我们将简单地迭代数组power23[]并计算范围[L, R] 中的数字。
下面是上述方法的实现:
C++
// C++ program to count the elements
// in the range [L, R] whose prime
// factors are only 2 and 3.
#include
using namespace std;
#define ll long long int
// Function which will calculate the
// elements in the given range
void calc_ans(ll l, ll r)
{
vector power2, power3;
// Store the current power of 2
ll mul2 = 1;
while (mul2 <= r) {
power2.push_back(mul2);
mul2 *= 2;
}
// Store the current power of 3
ll mul3 = 1;
while (mul3 <= r) {
power3.push_back(mul3);
mul3 *= 3;
}
// power23[] will store pairwise product of
// elements of power2 and power3 that are <=r
vector power23;
for (int x = 0; x < power2.size(); x++) {
for (int y = 0; y < power3.size(); y++) {
ll mul = power2[x] * power3[y];
if (mul == 1)
continue;
// Insert in power23][]
// only if mul<=r
if (mul <= r)
power23.push_back(mul);
}
}
// Store the required answer
ll ans = 0;
for (ll x : power23) {
if (x >= l && x <= r)
ans++;
}
// Print the result
cout << ans << endl;
}
// Driver code
int main()
{
ll l = 1, r = 10;
calc_ans(l, r);
return 0;
}
Java
// Java program to count the elements
// in the range [L, R] whose prime
// factors are only 2 and 3.
import java.util.*;
class GFG{
// Function which will calculate the
// elements in the given range
static void calc_ans(int l, int r)
{
Vector power2 = new Vector(),
power3 = new Vector();
// Store the current power of 2
int mul2 = 1;
while (mul2 <= r)
{
power2.add(mul2);
mul2 *= 2;
}
// Store the current power of 3
int mul3 = 1;
while (mul3 <= r)
{
power3.add(mul3);
mul3 *= 3;
}
// power23[] will store pairwise product of
// elements of power2 and power3 that are <=r
Vector power23 = new Vector();
for (int x = 0; x < power2.size(); x++)
{
for (int y = 0; y < power3.size(); y++)
{
int mul = power2.get(x) *
power3.get(y);
if (mul == 1)
continue;
// Insert in power23][]
// only if mul<=r
if (mul <= r)
power23.add(mul);
}
}
// Store the required answer
int ans = 0;
for (int x : power23)
{
if (x >= l && x <= r)
ans++;
}
// Print the result
System.out.print(ans + "\n");
}
// Driver code
public static void main(String[] args)
{
int l = 1, r = 10;
calc_ans(l, r);
}
}
// This code is contributed by 29AjayKumar
Python3
# Python3 program to count the elements
# in the range [L, R] whose prime
# factors are only 2 and 3.
# Function which will calculate the
# elements in the given range
def calc_ans(l, r):
power2 = []; power3 = [];
# Store the current power of 2
mul2 = 1;
while (mul2 <= r):
power2.append(mul2);
mul2 *= 2;
# Store the current power of 3
mul3 = 1;
while (mul3 <= r):
power3.append(mul3);
mul3 *= 3;
# power23[] will store pairwise
# product of elements of power2
# and power3 that are <=r
power23 = [];
for x in range(len(power2)):
for y in range(len(power3)):
mul = power2[x] * power3[y];
if (mul == 1):
continue;
# Insert in power23][]
# only if mul<=r
if (mul <= r):
power23.append(mul);
# Store the required answer
ans = 0;
for x in power23:
if (x >= l and x <= r):
ans += 1;
# Print the result
print(ans);
# Driver code
if __name__ == "__main__":
l = 1; r = 10;
calc_ans(l, r);
# This code is contributed by AnkitRai01
C#
// C# program to count the elements
// in the range [L, R] whose prime
// factors are only 2 and 3.
using System;
using System.Collections.Generic;
class GFG{
// Function which will calculate the
// elements in the given range
static void calc_ans(int l, int r)
{
List power2 = new List(),
power3 = new List();
// Store the current power of 2
int mul2 = 1;
while (mul2 <= r)
{
power2.Add(mul2);
mul2 *= 2;
}
// Store the current power of 3
int mul3 = 1;
while (mul3 <= r)
{
power3.Add(mul3);
mul3 *= 3;
}
// power23[] will store pairwise product of
// elements of power2 and power3 that are <=r
List power23 = new List();
for (int x = 0; x < power2.Count; x++)
{
for (int y = 0; y < power3.Count; y++)
{
int mul = power2[x] *
power3[y];
if (mul == 1)
continue;
// Insert in power23,]
// only if mul<=r
if (mul <= r)
power23.Add(mul);
}
}
// Store the required answer
int ans = 0;
foreach (int x in power23)
{
if (x >= l && x <= r)
ans++;
}
// Print the result
Console.Write(ans + "\n");
}
// Driver code
public static void Main(String[] args)
{
int l = 1, r = 10;
calc_ans(l, r);
}
}
// This code is contributed by 29AjayKumar
Javascript
输出:
6
时间复杂度: O(log 2 (R) * log 3 (R))
注意:该方法可以进一步优化。存储 2 和 3 的幂后,可以使用两个指针计算答案,而不是生成所有数字
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