方法1 (使用排序)

#include <iostream>

void quickSort(int *, int , int );

bool hasArrayTwoCandidates(int A [], int arrSize , int sum )
{
        int l, r;

        //对数组元素进行排序
       quickSort( A, 0, arrSize - 1);

        //在已排序数组中查找这两个元素
       l = 0;
       r = arrSize - 1;
        while (l < r)
       {
               if ( A[l] + A[r] == sum)
                      return 1;
               else if ( A[l] + A[r] < sum)
                     l++;
               else // A[i] + A[j] > sum
                     r--;
       }
        return 0;
}

int main()
{
        int A[] = { 1, 4, 45, 6, 10, -8 };
        int sum = 16;
        int arrSize = 6;

        if (hasArrayTwoCandidates(A, arrSize, sum))
              std::cout << "Array has two elements with sum 16\n" ;
        else
              std::cout << "Array doesn't have two elements with sum 16\n" ;

        return 0;
}

//下面的代码用于实现快速排序。
void exchange(int *a , int *b )
{
        int temp = * a;
       * a = * b;
       * b = temp;
}

//数组最后元素做为mid元素，进行排序
int partition(int A [], int si , int ei )
{
        int x = A[ ei];
        int i = ( si - 1);

        for ( int j = si; j <= ei - 1; j++)
       {
               if ( A[j] <= x)
              {
                     i++;
                     exchange(& A[i], & A[j]);
              }
       }
       exchange(& A[i + 1], & A[ ei]);
        return (i + 1);
}

/* 快速排序的实现
A[] --> Array to be sorted
si  --> Starting index
ei  --> Ending index
*/
void quickSort(int A [], int si , int ei )
{
        int pi;    //Partitioning index
        if ( si < ei)
       {
              pi = partition( A, si, ei);
              quickSort( A, si, pi - 1);
              quickSort( A, pi + 1, ei);
       }
}

方法2 (使用哈希表)

#include <iostream>

#define MAX 10000

void findPairs(int arr[], int arrSize, int sum)
{
	//定义并初始这个map
	bool binMap[MAX];
	memset(binMap, 0, sizeof(binMap) / sizeof(bool));

	for (int i = 0; i < arrSize; i++)
	{
		int temp = sum - arr[i];
		if (temp >= 0 && binMap[temp])
		{
			std::cout << "Pair with given sum " << sum << " is (" << arr[i] << ", " << temp << ")\n";
		}
		binMap[arr[i]] = true;
	}
}

int main()
{
	int A[] = { 1, 4, 45, 6, 10, 8 };
	int n = 53;
	int arr_size = sizeof(A) / sizeof(int);
	findPairs(A, arr_size, n);
	return 0;
}

哈希(5) - 检测数组A[]中是否存在元素对其和为x

原文：http://blog.csdn.net/shltsh/article/details/46485063