计算数组中总和在[a，b]
范围内的三元组的数量
原文:https://www . geeksforgeeks . org/count-数组中具有范围总和的三元组数量-a-b/
给定一个不同整数的数组和一个范围[a，b]，任务是计算具有在范围[a，b]内的和的三元组的数量。 例:
Input : arr[] = {8, 3, 5, 2}
range = [7, 11]
Output : 1
There is only one triplet {2, 3, 5}
having sum 10 in range [7, 11].
Input : arr[] = {2, 7, 5, 3, 8, 4, 1, 9}
range = [8, 16]
Output : 36
一种天真的方法是运行三个循环来逐个考虑所有的三元组。求每个三元组的和，如果和在给定的范围[a，b]内，则增加计数。 以下是上述办法的实施情况:
C++
// C++ program to count triplets with
// sum that lies in given range [a, b].
#include <bits/stdc++.h>
using namespace std;
// Function to count triplets
int countTriplets(int arr[], int n, int a, int b)
{
// Initialize result
int ans = 0;
// Fix the first element as A[i]
for (int i = 0; i < n - 2; i++) {
// Fix the second element as A[j]
for (int j = i + 1; j < n - 1; j++) {
// Now look for the third number
for (int k = j + 1; k < n; k++)
if (arr[i] + arr[j] + arr[k] >= a
&& arr[i] + arr[j] + arr[k] <= b)
ans++;
}
}
return ans;
}
// Driver Code
int main()
{
int arr[] = { 2, 7, 5, 3, 8, 4, 1, 9 };
int n = sizeof arr / sizeof arr[0];
int a = 8, b = 16;
cout << countTriplets(arr, n, a, b) << endl;
return 0;
}
Java 语言(一种计算机语言，尤用于创建网站)
// Java program to count triplets
// with sum that lies in given
// range [a, b].
import java.util.*;
class GFG
{
// Function to count triplets
public static int countTriplets(int []arr, int n,
int a, int b)
{
// Initialize result
int ans = 0;
// Fix the first
// element as A[i]
for (int i = 0; i < n - 2; i++)
{
// Fix the second
// element as A[j]
for (int j = i + 1; j < n - 1; j++)
{
// Now look for the
// third number
for (int k = j + 1; k < n; k++)
{
if (arr[i] + arr[j] + arr[k] >= a &&
arr[i] + arr[j] + arr[k] <= b)
{ans++;}
}
}
}
return ans;
}
// Driver Code
public static void main(String[] args)
{
int[] arr = { 2, 7, 5, 3, 8, 4, 1, 9 };
int n = arr.length;
int a = 8, b = 16;
System.out.println("" + countTriplets(arr, n,
a, b));
}
}
// This code is contributed
// by Harshit Saini
Python 3
# Python3 program to count
# triplets with sum that
# lies in given range [a, b].
# Function to count triplets
def countTriplets(arr, n, a, b):
# Initialize result
ans = 0
# Fix the first
# element as A[i]
for i in range(0, n - 2):
# Fix the second
# element as A[j]
for j in range(i + 1, n - 1):
# Now look for
# the third number
for k in range(j + 1, n):
if ((arr[i] + arr[j] + arr[k] >= a)
and (arr[i] + arr[j] + arr[k] <= b)):
ans += 1
return ans
# Driver code
if __name__ == "__main__":
arr = [ 2, 7, 5, 3, 8, 4, 1, 9 ]
n = len(arr)
a = 8; b = 16
print(countTriplets(arr, n, a, b))
# This code is contributed
# by Harshit Saini
C
// C# program to count triplets
// with sum that lies in given
// range [a, b].
using System;
class GFG
{
// Function to count triplets
public static int countTriplets(int []arr, int n,
int a, int b)
{
// Initialize result
int ans = 0;
// Fix the first
// element as A[i]
for (int i = 0;
i < n - 2; i++)
{
// Fix the second
// element as A[j]
for (int j = i + 1;
j < n - 1; j++)
{
// Now look for the
// third number
for (int k = j + 1;
k < n; k++)
{
if (arr[i] + arr[j] + arr[k] >= a &&
arr[i] + arr[j] + arr[k] <= b)
{ans++;}
}
}
}
return ans;
}
// Driver Code
public static void Main()
{
int[] arr = {2, 7, 5, 3, 8, 4, 1, 9};
int n = arr.Length;
int a = 8, b = 16;
Console.WriteLine("" + countTriplets(arr, n,
a, b));
}
}
// This code is contributed
// by Akanksha Rai(Abby_akku)
服务器端编程语言（Professional Hypertext Preprocessor 的缩写）
<?php
// PHP program to count triplets with
// sum that lies in given range [a, b].
// Function to count triplets
function countTriplets($arr, $n, $a, $b)
{
// Initialize result
$ans = 0;
// Fix the first element as A[i]
for ($i = 0; $i < $n - 2; $i++)
{
// Fix the second element as A[j]
for ($j = $i + 1; $j < $n - 1; $j++)
{
// Now look for the third number
for ($k = $j + 1; $k < $n; $k++)
if ($arr[$i] + $arr[$j] + $arr[$k] >= $a &&
$arr[$i] + $arr[$j] + $arr[$k] <= $b)
$ans++;
}
}
return $ans;
}
// Driver Code
$arr = array( 2, 7, 5, 3, 8, 4, 1, 9 );
$n = sizeof($arr);
$a = 8; $b = 16;
echo countTriplets($arr, $n, $a, $b) . "\n";
// This code is contributed
// by Akanksha Rai(Abby_akku)
?>
java 描述语言
<script>
// Javascript program to count triplets with
// sum that lies in given range [a, b].
// Function to count triplets
function countTriplets( arr, n, a, b)
{
// Initialize result
var ans = 0;
// Fix the first element as A[i]
for (var i = 0; i < n - 2; i++) {
// Fix the second element as A[j]
for (var j = i + 1; j < n - 1; j++) {
// Now look for the third number
for (var k = j + 1; k < n; k++)
if (arr[i] + arr[j] + arr[k] >= a
&& arr[i] + arr[j] + arr[k] <= b)
ans++;
}
}
return ans;
}
// Driver Code
var arr = [ 2, 7, 5, 3, 8, 4, 1, 9 ];
var n = arr.length;
var a = 8, b = 16;
document.write( countTriplets(arr, n, a, b) );
</script>
Output:
36
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