poj 1090 Chain

http://poj.org/problem?id=1090

　　简单格雷码加大数，最近想先看书，所以有空只是拿这些水题来练练手......

#include <cstdio>
#include <cstring>

const int mod = 1000000000;
int ans[40], dg;
bool r[1005];

void db(bool add){
    for (int i = 0; i < dg; i++){
        ans[i] <<= 1;
    }
    if (add){
        ans[0]++;
    }
    for (int i = 0; i < dg; i++){
        while (ans[i] >= mod){
            ans[i + 1]++;
            ans[i] -= mod;
        }
    }
    if (ans[dg]) dg++;
}

void print(){
    printf("%d", ans[dg - 1]);
    for (int i = dg - 2; i >= 0; i--){
        printf("%09d", ans[i]);
    }
}

void deal(int n){
    dg = 0;
    memset(ans, 0, sizeof(ans));
    for (int i = 0; i < n; i++){
        int a;

        scanf("%d", &a);
        r[i] = a ? true : false;
    }
    db(r[n - 1]);
    for (int i = n - 2; i >= 0; i--){
        r[i] = r[i + 1] ^ r[i];
        db(r[i]);
    }
    print();
    puts("");
}

int main(){
    int n;
#ifndef ONLINE_JUDGE
    freopen("in", "r", stdin);
#endif
    while (~scanf("%d", &n)){
       deal(n);
    }

    return 0;
}

——written by Lyon