zoj1245 Triangles(DP)

/*
动态三角形：每次DP时考虑的是两个子三角形的高度即可
注意：三角形可以是倒置的。
*/

View Code

 1 #include <iostream>
 2 #include <cstdlib>
 3 #include <cstring>
 4 #include <stdio.h>
 5 
 6 using namespace std;
 7 
 8 char  Tri[ 101 ][ 201 ];
 9 short Val[ 101 ][ 201 ];
10 
11 int main()
12 {
13     int n,cases = 1;
14     while ( scanf("%d",&n) && n ) {
15         getchar();
16         for ( int i = 0 ; i < n ; ++ i ) {
17             int m = 0;
18             while ( ( Tri[ i ][ m ] = getchar() ) != '\n' ) ++ m;
19         }
20         
21         memset( Val, 0, sizeof( Val ) );
22         for ( int i = 0 ; i < 2*n ; ++ i )
23             if ( Tri[ 0 ][ i ] == '#' )
24                 Val[ 0 ][ i ] = 0;
25             else
26                 Val[ 0 ][ i ] = 1;
27         for ( int i = 1 ; i < n ; ++ i )
28         for ( int j = i ; j < 2*n-1-i ; j += 2 )
29             if ( Tri[ i ][ j ] == '#' )
30                 Val[ i ][ j ] = 0;
31             else if ( Tri[ i-1 ][ j ] == '#' )
32                 Val[ i ][ j ] = 1;
33             else 
34                 Val[ i ][ j ] = 1+min( Val[ i-1 ][ j-1 ], Val[ i-1 ][ j+1 ] );
35         
36         if ( Tri[ n-2 ][ 2*n-3 ] == '#' )
37             Val[ n-2 ][ 2*n-3 ] = 0;
38         else
39             Val[ n-2 ][ 2*n-3 ] = 1;
40             
41         for ( int i = n-3 ; i >= 0 ; -- i )
42         for ( int j = i+1 ; j < 2*n-2-i ; j += 2 )
43             if ( Tri[ i ][ j ] == '#' )
44                 Val[ i ][ j ] = 0;
45             else if ( Tri[ i+1 ][ j ] == '#' )
46                 Val[ i ][ j ] = 1;
47             else
48                 Val[ i ][ j ] = 1+min( Val[ i+1 ][ j-1 ], Val[ i+1 ][ j+1 ] );
49                 
50         /*
51         for ( int i = 0 ; i < n ; ++ i ) {
52             for ( int j = 0 ; j < 2*n-i-1 ; ++ j )
53                 cout << Val[ i ][ j ] << " ";
54             cout << endl;
55         }
56         */
57         
58         int Max = 0;
59         for ( int i = 0 ; i < n ; ++ i )
60         for ( int j = i ; j < 2*n-i-1 ; ++ j )
61             if ( Val[ i ][ j ] > Max )
62                 Max = Val[ i ][ j ];
63         
64         cout << "Triangle #" << cases ++ << endl;
65         cout << "The largest triangle area is ";
66         cout << Max*Max << "." << endl << endl;
67     }
68     return 0;
69 }