USACO 2.1 Sorting A Three-Valued Sequence (sort3)

//Main Idear//The problem is quite easy, the key point is to consider all kinds of situation.//We first calculate the number of 1,2,3,namely, counter1,counter2,counter3//So, when the sequence is in non-decreasing order, number 1 shoud be in place(start from 0) //[0,counter1-1],2 in [counter1,counter1+counter2-1] and 3 in [counter1+counter2,sequence_lenght-1]//Then we can count then number in wrong place and use the min swap step to put them in order./*ID: haolink1PROG: sort3LANG: C++*///#include <iostream>#include <fstream>using namespace std;int main(){    ifstream fin("sort3.in");    short len = 0;    fin >> len;    short* numbers = new short[len];    for(short i = 0; i < len; i++){        fin >> numbers[i];    }    //calculate the number of 1,2,3 and store them in counter[0],counter[1],counter[2] respectively    short counter[3] = {0};    for(short i = 0; i < len; i++){       counter[numbers[i]-1]++;     }//    for(short i = 0; i < 3; i++){//        cout<<counter[i]<<endl;//    }    //caltulate the number in the wrong place.     //Eg: number 2, and 3 shoudn't appear in the palce that's lower then counter[0]    short num_2_in_1 = 0;    short num_3_in_1 = 0;    for(short i = 0; i< counter[0]; i++){        if(numbers[i] == 2)            num_2_in_1++;        if(numbers[i] == 3)            num_3_in_1++;    }    short num_1_in_2 = 0;    short num_3_in_2 = 0;    for(short i = counter[0]; i < counter[0]+counter[1]; i++){        if(numbers[i] == 1)            num_1_in_2++;        if(numbers[i] == 3)            num_3_in_2++;    }    short num_1_in_3 = 0;    for(short i =counter[0]+counter[1]; i < len; i++){        if(numbers[i] == 1)            num_1_in_3++;    }//    cout<<num_2_in_1<<" "<<num_3_in_1<<" "<<num_1_in_2<<" "<<num_3_in_2<<" "<<num_1_in_3<<endl;    //calculate the swap times we need to make the sequence in order.    short swap_num = 0;    if(num_2_in_1 > 0){        if(num_2_in_1 <=  num_1_in_2){            swap_num += num_2_in_1;            num_1_in_2 -= num_2_in_1;            num_2_in_1 = 0;        }else{            swap_num += num_1_in_2;            num_2_in_1 -= num_1_in_2;            num_1_in_2 = 0;        }        if(num_2_in_1 > 0){            swap_num += 2*num_2_in_1;            num_1_in_3 -= num_2_in_1;            num_3_in_2 -= num_2_in_1;            num_2_in_1 = 0;        }    }    if(num_3_in_1 > 0){        if(num_3_in_1 <= num_1_in_3){            swap_num += num_3_in_1;            num_1_in_3 -= num_3_in_1;            num_3_in_1 = 0;        }else{            swap_num += num_1_in_3;            num_3_in_1 -= num_1_in_3;            num_1_in_3 = 0;        }        if(num_3_in_1 > 0){            swap_num += 2*num_3_in_1;            num_1_in_2 -= num_3_in_1;            //num_2_in_3 -= num_3_in_1;            num_3_in_1 = 0;        }    }    if(num_3_in_2 > 0){        swap_num += num_3_in_2;      }    ofstream fout("sort3.out");    fout<<swap_num<<endl;    delete[] numbers;    return 0;}