POJ 1656 二维树状数组

题意：给定100*100的网格，每个格子可以涂上黑色或者白色（初始时全部树白色），经过一系列操作后输出任意一个正方形区域内的黑色格子数。

#include <iostream>
using namespace std;

int c[110][110];
int a[110][110];
const int n = 100;

int lowbit ( int x )
{
return x & ( -x );
}

void modify ( int x, int y, int v )
{
for ( int i = x; i <= n; i += lowbit(i) )
{
for ( int j = y; j <= n; j += lowbit(j) )
c[i][j] += v;
}
}

void update ( int x, int y, int l, int mark )
{
int x1 = x, x2 = x + l - 1, y1 = y, y2 = y + l - 1;
for ( int i = x1; i <= x2; ++i )
{
for ( int j = y1; j <= y2; ++j )
{
if ( a[i][j] != mark )
{
a[i][j] = mark;
modify ( i, j, mark );
}
}
}
}

int sum ( int x, int y )
{
int total = 0;
for ( int i = x; i > 0; i -= lowbit(i) )
{
for ( int j = y; j > 0; j -= lowbit(j) )
total += c[i][j];
}
return total;
}

int getSum ( int x, int y, int l )
{
int x1 = x, y1 = y, x2 = x + l - 1, y2 = y + l - 1;
return sum ( x2, y2 ) - sum ( x1-1, y2 ) - sum( x2 , y1 - 1 ) + sum ( x1 - 1, y1 - 1);
}

int main()
{
int t, x, y, l;
char oper[10];
memset(c,0,sizeof(c));
memset(a,-1,sizeof(a));
scanf("%d", &t );
while ( t-- )
{
scanf("%s", oper );
scanf("%d%d%d", &x, &y, &l );
if ( strcmp(oper, "BLACK") == 0 )
update ( x, y, l, 1 );
else if ( strcmp(oper, "WHITE") == 0 )
update ( x, y, l, -1 );
else
printf ( "%d\n", getSum ( x, y, l ) );
}
return 0;
}


此题直接求解0MS

#include <iostream>
using namespace std;

int a[110][110];

void update ( int x1, int y1, int x2, int y2, bool mark )
{
for ( int i = x1; i <= x2; ++i )
for ( int j = y1; j <= y2; ++j )
a[i][j] = mark;
}

int getSum ( int x1, int y1, int x2, int y2 )
{
int i, j, sum = 0;
for ( i = x1; i <= x2; ++i )
for ( j = y1; j <= y2; ++j )
if ( a[i][j] )
++sum;
return sum;
}

int main()
{
int t, x, y, l;
char oper[10];
memset(a,0,sizeof(a));
scanf("%d", &t );
while ( t-- )
{
scanf("%s", oper );
scanf("%d%d%d", &x, &y, &l );
if ( strcmp(oper, "BLACK") == 0 )
update ( x, y, x+l-1, y+l-1, 1 );
else if ( strcmp(oper, "WHITE") == 0 )
update ( x, y, x+l-1, y+l-1, 0 );
else
printf ( "%d\n", getSum ( x, y, x+l-1, y+l-1 ) );
}
return 0;
}