两个有序数组求中位数

#include <vector>
using std::vector;
typedef int Comparable;
//#include <iostream>
//#include <cstdlib>
//using std::cout;
Comparable find_median(const Comparable *arrA, int lenA, const Comparable *arrB, int lenB) {
//  static int record = 0;
//  ++record;
//  if (record % 100 == 0) {
//    system("pause");
//  }
//  cout << "Times " << record << "\narrA: ";
//  for (int i = 0; i < lenA; ++i) {
//    cout << arrA[i] << ‘ ‘;
//  }
//  cout << ‘\n‘;
//  cout << "arrB: ";
//  for (int i = 0; i < lenB; ++i) {
//    cout << arrB[i] << ‘ ‘;
//  }
//  cout << "\n\n";

  if (lenA == lenB && lenA == 1) {
    return (*arrA > *arrB ? *arrB: *arrA);
  }
  int midA = (lenA - 1) / 2;
  int midB = (lenB - 1) / 2;
  if (lenA == 1) {
    if (lenB % 2 == 1) {
      if (arrA[0] >= arrB[midB]) {
        return arrB[midB];
      } else if (arrA[0] <= arrB[midB - 1]) {
        return arrB[midB - 1];
      } else {
        return arrA[0];
      }
    } else {
      if (arrA[0] >= arrB[midB + 1]) {
        return arrB[midB + 1];
      } else if (arrA[0] <= arrB[midB]) {
        return arrB[midB];
      } else {
        return arrA[0];
      }
    }
  } else if (lenB == 1) {
    return find_median(arrB, lenB, arrA, lenA);
  }
  int l = (midA <= midB? midA: midB);
  //cout << "l: " << l << " midA: " << midA << " midB: " << midB << ‘\n‘;
  if (lenA == 2 || lenB == 2) {  // 
    ++l;
  }
  if (arrA[midA] == arrB[midB]) {
    return arrA[midA];
  } else if (arrA[midA] < arrB[midB]) {
    return find_median(arrA + l, lenA - l, arrB, lenB - l);
  } else {
    return find_median(arrA, lenA - l, arrB + l, lenB - l);
  }
}

Comparable find_median (const vector<Comparable> &l1, const vector<Comparable> &l2) {
  return find_median(&l1[0], l1.size(), &l2[0], l2.size() );
}

// 下面这个是O(n)版本，用于检测正确性
using std::vector;
Comparable find_median2(const vector<Comparable> &l1, const vector<Comparable> &l2) {
  vector<Comparable>::const_iterator it1, it2;
  it1 = l1.begin();
  it2 = l2.begin();
  unsigned int mid = (l1.size() + l2.size() - 1) / 2;
  unsigned int k = 0;
  while (k < mid && it1 != l1.end() && it2 != l2.end()) {
    if (*it1 <= *it2) {
      ++it1;
    } else {
      ++it2;
    }
    ++k;
  }
  while (it1 != l1.end() && k < mid) {
    ++it1;
    ++k;
  }
  while (it2 != l2.end() && k < mid) {
    ++it2;
    ++k;
  }
  if (it1 == l1.end()) {
    return *it2;
  } else if (it2 == l2.end()) {
    return *it1;
  } else {
    return (*it1 < *it2? *it1: *it2);
  }
}

// 测试程序
#include <algorithm>
#include <iostream>
#include <ctime>
#include <cstdlib>
using std::cout;
using std::sort;
int main() {
  //vector<Comparable> l1 = {1, 2, 4.2, 7, 56};
  vector<Comparable> l1;
  vector<Comparable> l2;
  srand(time(0));
  int N = 100;  // 测试样例个数
  while (N--) {
    l1 = vector<Comparable>(rand() % 4 + 1);
    l2 = vector<Comparable>(rand() % 4 + 1);
    for (auto &i : l2) {
      i = rand() % 100;;
    }
    for (auto &i : l1) {
      i = rand() % 100;
    }
    sort(l1.begin(), l1.end());
    sort(l2.begin(), l2.end());
    int m1 = find_median(l1, l2);
    int m2 = find_median2(l1, l2);
    cout << m1 << ‘\n‘;
    cout << m2 << ‘\n‘;
    if (m1 != m2) {
      system("pause");
    }
  }
}