USACO 1.5 Number Triangles

USACO 1.5 Number Triangles

简单的dp题
由于每次只用到tri[n-1]的信息，所以可以优化为空间复杂度为O(n)，但代码要复杂得一些。keep it simple,:-)

#include  < iostream >
#include  < fstream >

using   namespace  std;

ifstream fin( " numtri.in " );
ofstream fout( " numtri.out " );

#ifdef _DEBUG
#define  out cout
#define  in cin
#else
#define  out fout
#define  in fin
#endif

int  tri[ 1000 ][ 1000 ];

void  solve()
{
     int  r;
     in >> r;
    
     for ( int  i = 0 ;i < r; ++ i){
         for ( int  j = 0 ;j < i + 1 ; ++ j){
             in >> tri[i][j];
        }
    }

     // 处理一下边界
     for ( int  i = 1 ;i < r; ++ i){
        tri[i][ 0 ] += tri[i - 1 ][ 0 ];
        tri[i][i] += tri[i - 1 ][i - 1 ];
    }

     for ( int  i = 2 ;i < r; ++ i){
         for ( int  j = 1 ;j < i; ++ j){
            tri[i][j] += max(tri[i - 1 ][j - 1 ],tri[i - 1 ][j]);
        }
    }

     int  res  =  INT_MIN;

     for ( int  i = 0 ;i < r; ++ i){
        res  =  max(res,tri[r - 1 ][i]);
    }

     out << res << endl;
}

int  main( int  argc, char   * argv[])
{
  solve();
   return   0 ;
}