求两个等长的有序序列的中位数（2011计算机统考试题）

/********************************************************************
    created:    2014/01/05
    created:    22:01
    file base:    main
    file ext:    cpp
    author:        Justme0 (http://blog.csdn.net/Justme0)
    
    purpose:    求两个等长的有序序列的中位数，时间复杂度O(log(n))
*********************************************************************/

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <vector>
#include <cassert>
#include <algorithm>
using namespace std;

template <class Iterator>
Iterator search_middle(Iterator begin1, Iterator end1, Iterator begin2) {
    while (begin1 + 1 != end1) {
        int len = end1 - begin1;
        int m = (len - 1) / 2;    // m 是中位数的下标
        bool is_odd = (len % 2 == 1);

        if (begin1[m] < begin2[m]) {
            if (is_odd) {
                begin1 += m;
            } else {
                begin1 += m + 1;
            }
        } else if (begin2[m] < begin1[m]) {
            if (is_odd) {
                begin2 += m;
                end1 -= m;
            } else {
                begin2 += m + 1;
                end1 -= m + 1;
            }
        } else {
            return begin1 + m;
        }
    }

    return *begin1 < *begin2 ? begin1 : begin2;
}

void input(vector<int> &v, int len) {
    for (int i = 0; i < len; ++i) {
        int elem;
        cin >> elem;
        v.push_back(elem);
    }
}

void output(vector<int> &v) {
    for (vector<int>::iterator it = v.begin(); it != v.end(); ++it) {
        cout << *it << " ";
    }
    cout << endl;
}

int main(int argc, char **argv) {
    freopen("cin.txt", "r", stdin);

    int len;
    while (cin >> len) {
        vector<int> v1, v2;
        input(v1, len);
        input(v2, len);

        vector<int> v3(v1.size() * 2);
        merge(v1.begin(), v1.end(), v2.begin(), v2.end(), v3.begin());
        int b = v3[(v3.size() - 1) / 2];

        int a = *search_middle(v1.begin(), v1.end(), v2.begin());
        assert(a == b);
        cout << a << " " << b << endl;
        if(a != b) {
            output(v3);
            cout << "a=" << a << endl;
            cout << "b=" << b << endl;
        }
    }

    return 0;
}

/* cin.txt
1
1
0

1
-3
3

2
1 2
2 3

3
0 5 6
2 2 2

4
1 2 3 4
6 7 8 9

4
1 2 6 7
3 4 5 6

5
12 22 222 333 3333
10 13 44 55 66

10
3 3 22 34 44 333 2222 11111 11112 11113
-5 -4 0 1 444 4444 44444 44445 444444 444445
*/