Javascript程序计算给定总和的对

给定一个整数数组和一个数字“sum”，找出数组中总和等于“sum”的整数对的数量。

例子：

Input  :  arr[] = {1, 5, 7, -1}, 
          sum = 6
Output :  2
Pairs with sum 6 are (1, 5) and (7, -1)

Input  :  arr[] = {1, 5, 7, -1, 5}, 
          sum = 6
Output :  3
Pairs with sum 6 are (1, 5), (7, -1) &
                     (1, 5)         

Input  :  arr[] = {1, 1, 1, 1}, 
          sum = 2
Output :  6
There are 3! pairs with sum 2.

Input  :  arr[] = {10, 12, 10, 15, -1, 7, 6, 
                   5, 4, 2, 1, 1, 1}, 
          sum = 11
Output :  9

预期时间复杂度 O(n)

朴素的解决方案——一个简单的解决方案是遍历每个元素并检查数组中是否有另一个数字可以添加到它以得出总和。

Javascript

  
// Javascript implementation of simple method to find count of
// pairs with given sum.
  
// Returns number of pairs in arr[0..n-1] with sum equal
// to 'sum'
function getPairsCount(arr, n, sum)
{
    let count = 0; // Initialize result
  
    // Consider all possible pairs and check their sums
    for (let i = 0; i < n; i++)
        for (let j = i + 1; j < n; j++)
            if (arr[i] + arr[j] == sum)
                count++;
  
    return count;
}
  
// Driver function to test the above function
    let arr = [ 1, 5, 7, -1, 5 ];
    let n = arr.length;
    let sum = 6;
    document.write("Count of pairs is "
        + getPairsCount(arr, n, sum));
      
// This code is contributed by Mayank Tyagi
  

输出

Count of pairs is 3

时间复杂度： O(n ² )
辅助空间： O(1)

有关详细信息，请参阅有关给定总和的计数对的完整文章！