BestCoder Round #8

Summary

/*
ID:esxgx1
LANG:C++
PROG:bestcoder8_A
*/
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;

int a[107];
long long b[107*107];

int main(void)
{
    #ifndef ONLINE_JUDGE
    freopen("in.txt", "r", stdin);
    #endif

    int N;
    while(scanf("%d", &N) > 0) {
        for(int i=0; i<N; ++i) scanf("%I64d", &a[i]);
        int k = 0;
        for(int i=0; i<N; ++i) {
            for(int j=i+1; j<N; ++j) {
                b[k++] = a[i] + a[j];
            }
        }
        sort(b, b+k);
        int j = unique(b, b+k) - b;
        long long S = 0;
        for(int i=0; i<j; ++i) {
            S += b[i];
        }
        printf("%I64d
", S);
    }
    return 0;
}

Reading comprehension

/*
ID:esxgx1
LANG:C++
PROG:bestcoder8_B
*/
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;

int M;

const int n = 2;
struct mat {
    int at[n][n];
};

#define mod M
mat m22_m(const mat &a,const mat &b)
{
    mat t;
    for(int i=0;i<n;++i) {
        for(int k=0;k<n;++k) {
            long long u = 0;
            for(int j=0;j<n;++j)
                u += (long long)a.at[i][j] * b.at[j][k];
            t.at[i][k] = u % mod;
        }
    }
    return t;
}

mat expo(mat p,int k)
{
    mat e;
    memset(e.at,0,sizeof(e.at));
    for(int i=0; i<n; ++i) e.at[i][i]=1;
    for(;k; k>>=1) {
        if(k & 1) e = m22_m(e, p);
        p = m22_m(p,p);
    }
    return e;
}

inline void DEC(int &a, int b){a -= b; if (a < 0) a += M;}

int main(void)
{
    #ifndef ONLINE_JUDGE
    freopen("in.txt", "r", stdin);
    #endif

    int N;
    while(scanf("%d%d", &N, &M)>=0) {
        mat p;
        p.at[0][0] = 1, p.at[0][1] = 2;
        p.at[1][0] = 1, p.at[1][1] = 0;
        int rslt = expo(p, N).at[0][0];
        if (!(N&1)) DEC(rslt, 1);
        printf("%d
", rslt);
    }
    return 0;
}