USACO-Section1.3 Combination Lock

Combination Lock

2017.06.01

题解

搜索，按条件剪枝即可，注意搜索最后要再次检验数字是否符合同一个密码的条件。

代码

/*ID: xhzdcyy1PROB: comboLANG: C++         */#include <iostream>#include <fstream>#include <string>#include <algorithm>#define cin fin#define cout fout using namespace std;ofstream fout ("combo.out");ifstream fin ("combo.in");int N;int res=0;int a[3],b[3],c[3];int abs(int a,int b){    return a-b>0?a-b:b-a;}bool check(int t[],int i){    int left=t[i]-2;    if(left<=0) left+=N;    int right=t[i]+2;    if(right>N) right-=N;    if(left<right){        if(c[i]<left||c[i]>right) return false;    }    else{        if(c[i]>right&&c[i]<left) return false;    }    return true;}void func(int n){    if(n==3){        if(check(a,0)&&check(a,1)&&check(a,2)) ++res;        else if(check(b,0)&&check(b,1)&&check(b,2)) ++res;        return;    }    for(int i=0;i<N;i++){        c[n]=i;        if(check(a,n)||check(b,n))            func(n+1);    }}int main(){    int tmp;    cin>>N;    for(int i=0;i<3;i++){        cin>>a[i];    }    for(int i=0;i<3;i++){        cin>>b[i];    }    func(0);    cout<<res<<endl;     return 0; }