UVA 10519 !! Really Strange !!

来源：互联网发布：qq飞车青峰剃刀数据编辑：程序博客网时间：2024/05/29 17:25

题意：n个圆两两相交，将平面分成了几部分，假设已有n-1个圆，那么第n个圆将与前n-1个圆相交2*(n-1)个点，也就是2*(n-1)个弧，而一个弧将产生出一个新的部分，所以：

f(n) = f(n-1) + 2*(n-1),推出公式:f(n) = n^2-n+2,大数，害我错了好几次的是：n=0时的特判

#include <iostream>#include <cstdio>#include <cstring>#include <cmath>#include <algorithm>using namespace std;const int MAXN = 1000000;char n[MAXN];long long p[MAXN],ans[MAXN]; // f(n) = n^2-n+2 // f(0) = 1void pow_big(long long *a,long long *b,int &len){    int i,j;    for (i = 0; i < len; i++)        for (j = 0; j < len; j++)            ans[i+j] += a[i] * b[j];    len *= 2;    for (i = 0; i < len; i++){        ans[i+1] += ans[i] / 10;        ans[i] %= 10;    }    while (ans[len] == 0)        len--;    len++;}void cal(long long *b,int &len){    int i,c=0;    ans[0] += 2;    if (ans[0] >= 10){        ans[1] += ans[0] / 10;        ans[0] %= 10;    }    for (i = 0; i < len; i++){        ans[i] = ans[i] - b[i] + c;        if (ans[i] < 0){            ans[i] += 10;            c = -1;        }        else c = 0;    }     while (ans[len-1] == 0)        len--;}int main(){    while (scanf("%s",n) != EOF){        memset(p,0,sizeof(p));        memset(ans,0,sizeof(ans));        int len = strlen(n);        for (int i = 0; i < len; i++)            p[i] = n[len-1-i] - '0';        if (p[0] == 0){            printf("1\n");            continue;        }        pow_big(p,p,len);        cal(p,len);        for (int i = len-1; i >= 0; i--)            printf("%lld",ans[i]);        printf("\n");    }    return 0;}