求一个数组中重复数字的个数，要求复杂度为O(n)

给出代码

#include <stdio.h>
#include <unistd.h>
#include <iostream>
#include <memory.h>
#include <string.h>

int main()
{
        typedef int data_type;
        data_type a[] = {1,4,6,7,7,8,4,9,1,7,6,4,1,2,0,0};

        const char* hint = "The original number is:\n ";
        write(STDOUT_FILENO, hint, strlen(hint));
        for(int i = 0; i < sizeof(a)/sizeof(a[0]); ++i)
        {
                printf("%d ", a[i]);
        }
        printf("\n");

        // get the max value
        int max = a[0];
        for(int i = 0;i < sizeof(a)/sizeof(data_type);++i)
        {
                if(a[i] > max)
                {
                        max = a[i];
                }
        }

        // allocate an space. you can use bitwise if the space is too big.
        data_type* p = new data_type[max + 1];
        memset(p, 0, max + 1);

        int cnt = 0;
        for(int i = 0;i < sizeof(a)/sizeof(data_type);++i)
        {
                if(*(p + a[i]) == -1)
                {
                        ++cnt;
                }
                else
                {
                        *(p + a[i]) = -1;
                }
        }

        std::cout << "The dumplicated number is " << cnt << std::endl;

        return 0;
}

　　

编译执行

[root@ba algr]# g++ array.cpp -g
[root@ba algr]# ./a.out 
The original number is:
 1 4 6 7 7 8 4 9 1 7 6 4 1 2 0 0 
The dumplicated number is 8
[root@ba algr]#