Quadtrees UVA297

 Quadtrees 

A quadtree is a representation format used to encode images. The fundamental idea behind the quadtree is that any image can be split into four quadrants. Each quadrant may again be split in four sub quadrants, etc. In the quadtree, the image is represented by a parent node, while the four quadrants are represented by four child nodes, in a predetermined order.

Of course, if the whole image is a single color, it can be represented by a quadtree consisting of a single node. In general, a quadrant needs only to be subdivided if it consists of pixels of different colors. As a result, the quadtree need not be of uniform depth.

A modern computer artist works with black-and-white images of  units, for a total of 1024 pixels per image. One of the operations he performs is adding two images together, to form a new image. In the resulting image a pixel is black if it was black in at least one of the component images, otherwise it is white.

This particular artist believes in what he calls the preferred fullness: for an image to be interesting (i.e. to sell for big bucks) the most important property is the number of filled (black) pixels in the image. So, before adding two images together, he would like to know how many pixels will be black in the resulting image. Your job is to write a program that, given the quadtree representation of two images, calculates the number of pixels that are black in the image, which is the result of adding the two images together.

In the figure, the first example is shown (from top to bottom) as image, quadtree, pre-order string (defined below) and number of pixels. The quadrant numbering is shown at the top of the figure.

Input Specification

The first line of input specifies the number of test cases (N) your program has to process.

The input for each test case is two strings, each string on its own line. The string is the pre-order representation of a quadtree, in which the letter 'p' indicates a parent node, the letter 'f' (full) a black quadrant and the letter 'e' (empty) a white quadrant. It is guaranteed that each string represents a valid quadtree, while the depth of the tree is not more than 5 (because each pixel has only one color).

Output Specification

For each test case, print on one line the text 'There are X black pixels.', where X is the number of black pixels in the resulting image.

Example Input

3ppeeefpffeefepefepeefepeeefpeefepeeefpeepefefe

Example Output

There are 640 black pixels.There are 512 black pixels.There are 384 black pixels.

这道题不是很难，但是花费了挺长的一段时间的，思路很明确就是递归建树，然后递归遍历两棵树，求解。

在写代码的过程中由于没搞清楚+和<<的优先级导致wa，后来才发现。

#include<iostream>#include<string>using namespace std;class node{public:char data;node *r1,*r2,*r3,*r4;};int sum,t;node* CreateTree(string s,int &x){++x;if(x==s.size()) return NULL;node *root=new node();root->data=s[x];if(s[x]=='p'){root->r1=CreateTree(s,x);root->r2=CreateTree(s,x);root->r3=CreateTree(s,x);root->r4=CreateTree(s,x);}return root;}void dfs(node *root1,node *root2,int s){    if(root1==NULL&&root2==NULL) return;    if(root1->data=='p'&&root2->data=='p')    {        dfs(root1->r1,root2->r1,s+1);        dfs(root1->r2,root2->r2,s+1);        dfs(root1->r3,root2->r3,s+1);        dfs(root1->r4,root2->r4,s+1);        return;    }    if(root1->data=='p'&&root2->data!='p')    {        dfs(root1->r1,root2,s+1);        dfs(root1->r2,root2,s+1);        dfs(root1->r3,root2,s+1);        dfs(root1->r4,root2,s+1);        return;    }    else if(root1->data!='p'&&root2->data=='p')    {        dfs(root1,root2->r1,s+1);        dfs(root1,root2->r2,s+1);        dfs(root1,root2->r3,s+1);        dfs(root1,root2->r4,s+1);        return;    }    else if(root1->data=='f'||root2->data=='f')    {        sum=sum+(1024>>(s*2));        return;    }}int main(){int n;cin>>n;cin.get();while(n--){string str1,str2;getline(cin,str1);getline(cin,str2);node *root1=new node;node *root2=new node;int pos1=-1,pos2=-1;sum=0;root1=CreateTree(str1,pos1);root2=CreateTree(str2,pos2);dfs(root1,root2,0);cout<<"There are "<<sum<<" black pixels."<<endl;}return 0;}