白书第二章上机练习

approximation.c

/* Chapter 02 - approximation */
#include <stdio.h>

int main(void)
{
	int i = 0;
	double pi_4 = 0.0, t = 0.0;
	
	i = 1;
	while( (t=1.0/(2*i-1)) >= 0.000001 )
		pi_4 += ( (i++%2) ? 1 : -1 ) * t;
		
	return !printf("%lf\n", pi_4);
}

daffodil.c

/* Chapter 02 - daffodil */
#include <stdio.h>

int main(void)
{
	int a = 0, b = 0, c = 0;
	for(a = 1;a < 10;a++)
		for(b = 0;b < 10;b++)
			for(c = 0;c < 10;c++)
				if( (100*a+10*b+c) == (a*a*a+b*b*b+c*c*c) )
					printf("%d%d%d ", a, b, c);
	return !printf("\n");
}

decimal.c

/* Chapter 02 - decimal */
#include <stdio.h>
#include <string.h>

int main(void)
{
	int i = 0, j = 0;
	int a = 0, b = 0, c = 0;
	char r[20];
	
	scanf("%d %d %d", &a, &b, &c);
	sprintf(r, "%lf", (double)a/(double)b);
	for(i = 0;i < strlen(r);i++)
	{
		if( r[i] == '.' )
		{
			for(j = 0;j < c;j++)
				if( i+j > strlen(r)-1 )
					putchar('0');
				else
					putchar(r[i+j]);
			if( j > strlen(r)-1 )
				putchar('0');
			else if ( i+j+1 > strlen(r)-1 )
				putchar(r[i+j]);
			else
				putchar(r[i+j]+((r[i+j+1]>'4')?1:0));
			
			return !printf("\n");
		}
		else
			putchar(r[i]);
	}
	
	return !printf("\n");
}

digit.c

/* Chapter 02 - digit */
#include <stdio.h>

int main(void)
{
	int i = 0;
	int num = 0;
	scanf("%d", &num);
	while(num >= 1)
		i += (num/=10)||1;
	return !printf("%d\n", i);
}

hanxin.c

/* Chapter 02 - hanxin */
#include <stdio.h>

int main(void)
{
	int i = 0;
	int a = 0, b = 0, c = 0;
	scanf("%d %d %d", &a, &b, &c);
	for(i = 10;i < 101;i++)
		if( (i%3==a) && (i%5==b) && (i%7==c) )
			return !printf("%d\n", i);
	return !printf("No answer\n");
}

harmony.c

/* Chapter 02 - harmony */
#include <stdio.h>
#include <math.h>

int main(void)
{
	int i = 0;
	int n = 0;
	double sum = 0.0;
	
	scanf("%d", &n);
	for(i = 1;i < n+1;i++)
		sum += 1.0 / (double)i;
	
	return !printf("%.3lf\n", sum);
}

permutation.c

/* Chapter 02 - premutation */
#include <stdio.h>

#define JOIN(a,b,c) ( (a)*100 + (b)*10 + (c) )

void solve(int start, int end, int top);

int s[9] = {1,2,3,4,5,6,7,8,9};
int n[9] = {0};

int main(void)
{
	int i = 0;
	
	/* 既然不必太动脑筋.. */
	solve(0, 8, 0);
	
	return 0;
}

void swap(int *a, int *b)
{
	int t = *a;
	*a = *b;
	*b = t;
}

void solve(int start, int end, int top)
{
	if( start == end )
	{
		int i = 0, j = 0, k = 0;
		*(n+top) = *(s+start);
		i = JOIN(*(n+0), *(n+1), *(n+2));
		j = JOIN(*(n+3), *(n+4), *(n+5));
		k = JOIN(*(n+6), *(n+7), *(n+8));
		if( j==2*i && k==3*i )
			printf("%d,%d,%d\n", i, j, k);
	} else {
		int i = 0;
		for(i = start;i < end+1;i++)
		{
			*(n+top) = *(s+i);
			swap(s+start, s+i);
			solve(start+1, end, top+1);
			swap(s+i, s+start);
		}
	}
}

stat.c

/* Chapter 02 - stat */
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
	int i = 0;
	int n = 0, m = 0;
	int *a = NULL;
	int count = 0;
	
	scanf("%d", &n);
	a = (int *)malloc( n * sizeof(int) );
	for(i = 0;i < n;i++)
		scanf("%d", a+i);
	scanf("%d", &m);
	
	for(i = 0;i < n;i++)
		if( *(a+i) < m )
			count++;
	
	return !printf("%d\n", count);
}

subsequence.c

/* Chapter 02 - subsequence */
#include <stdio.h>

int main(void)
{
	int i = 0;
	int n = 0, m = 0;
	double sum = 0.0;
	
	scanf("%d %d", &n, &m);
	for(i = n;i < m+1;i++)
		sum += 1.0/i/i;   // 考虑到i*i可能溢出
		
	return !printf("%.5lf\n", sum);
}

triangle.c

/* Chapter 02 - triangle */
#include <stdio.h>

int main(void)
{
	int i = 0, j = 0;
	int n = 0;
	
	scanf("%d", &n);
	for(i = 0;i < n;i++)
	{
		for(j = i;j > 0;j--)
			printf(" ");
		for(j = 0;j < (2*n-1-2*i);j++)
			printf("#");
		printf("\n");
	}
	
	return 0;
}