USACO 1.3 Barn Repair (barn1)

/*ID: haolink1PROG: barn1LANG: C++*///#include <iostream>#include <fstream>#include <list>using namespace std;bool CompareInterval(int free_interval_1, int free_interval_2){    if(free_interval_1 <= free_interval_2)        return true;    else        return false;}// by increasement order, T(n)=O(n^2)void InsertionSort(int* array, int length) {    for (int j = 1; j < length; j++) {            int key = array[j];            int i = j - 1;            while (i >= 0 && array[i] > key) {                    array[i + 1] = array[i];                    i--;            }            array[i + 1] = key;    }}int main(){    ifstream fin("barn1.in");    int max_boards = 0;    int total_stalls = 0;    int occupied_stalls = 0;    fin >> max_boards;    fin >> total_stalls;    fin >> occupied_stalls;    //count the number of serial occupied-stall interval     int serial_interval_num = 0;    list<int> free_intervals;    int cur_occupied = 0;    int prev_occupied = 0;    int* occupied_stall_position = new int[occupied_stalls];     for(int i = 0; i < occupied_stalls; i++){        fin >> occupied_stall_position[i];    }    //sort the position in ascending order    InsertionSort(occupied_stall_position,occupied_stalls);     for(int i = 0; i < occupied_stalls; i++){        cur_occupied = occupied_stall_position[i];        //note the way to count the serial interval number, while cur_occupied is exception;        if(cur_occupied == 1 || prev_occupied+1 != cur_occupied){            serial_interval_num++;            if(prev_occupied != 0)//the free interval made of the free stall before the first occupied stall is meaningless                free_intervals.push_back(cur_occupied - prev_occupied -1);         }        prev_occupied = cur_occupied;    }    int stalls_blocked = occupied_stalls;    if(serial_interval_num > max_boards){        free_intervals.sort(CompareInterval);        for(int i = 0; i < serial_interval_num - max_boards; i++){            stalls_blocked += free_intervals.front();            free_intervals.pop_front();        }    }    ofstream fout("barn1.out");    fout << stalls_blocked <<endl;    delete[] occupied_stall_position;    return 0;}