《Cracking the Coding Interview》——第18章：难题——题目9

2014-04-29 04:18

题目：有一连串的数被读入，设计一个数据结构，能随时返回当前所有数的中位数。

解法：用一个大顶堆，一个小顶堆将数分成数量最接近的两份，就能轻松得到中位数了。

代码：

 // 18.9 A stream of integers are passed to you, you have to tell me the median as they keep coming in.
 #include <climits>
 #include <iostream>
 #include <vector>
 #include <queue>
 using namespace std;

 template <class T>
 struct LessFunctor
 {
     bool operator() (const T &x, const T &y)
     {
         return x < y;
     }
 };

 template <class T>
 struct GreaterFunctor
 {
     bool operator() (const T &x, const T &y)
     {
         return x > y;
     }
 };

 template <class T>
 class MedianArray {
 public:
     MedianArray() {
         n_small = ;
         n_great = ;
     };

     void push(const T& val) {
         if (n_great == ) {
             greater_heap.push(val);
             ++n_great;
             return;
         }

         if (n_great > n_small) {
             smaller_heap.push(val);
             ++n_small;
         } else {
             greater_heap.push(val);
             ++n_great;
         }

         if (greater_heap.top() < smaller_heap.top()) {
             T tmp;

             tmp = greater_heap.top();
             greater_heap.pop();
             greater_heap.push(smaller_heap.top());
             smaller_heap.pop();
             smaller_heap.push(tmp);
         }
     };

     T median() {
         if (n_great == ) {
             return INT_MIN;
         } else if (n_great > n_small) {
             return greater_heap.top();
         } else {
             return (smaller_heap.top() + greater_heap.top()) / ;
         }
     };

     ~MedianArray() {
         n_small = ;
         n_great = ;
         while (!greater_heap.empty()) {
             greater_heap.pop();
         }
         while (!smaller_heap.empty()) {
             smaller_heap.pop();
         }
     };
 private:
     int n_small;

     // greater elements are stored in here.
     priority_queue<T, vector<T>, GreaterFunctor<T> > greater_heap;

     int n_great;

     // smaller elements are stored in here.
     priority_queue<T, vector<T>, LessFunctor<T> > smaller_heap;
 };

 int main()
 {
     MedianArray<int> ma;
     int val;

     while (cin >> val) {
         ma.push(val);
         cout << ma.median() << endl;
     }

     return ;
 }