统计数组中每个元素出现的个数，时间复杂度 O(n),空间 O(1)

代码如下：

#include <iostream>
using namespace std;

void work(int a[], int n)
{
    int i = 0;
    while(i < n)
    {
        int temp = a[i] - 1;
        if(temp < 0)
        {
            i++;
            continue;
        }
        if(a[temp] > 0)
        {
            a[i] = a[temp];
            a[temp] = -1;
        }
        else
        {
            a[temp]--;
            a[i] = 0;
        }
    }
}

int main()
{
    int n = 10;
        int *a = new int[n];
        for(int i = 0; i < n; i++)
            cin >> a[i];
        work(a, n);
        for(int i = 0; i < n; i++)
            if(a[i] < 0)
                cout << i + 1 << " " << (-a[i]) << endl;
        cout << "********************" << endl;
        delete[] a;
    
    return 0;
}