程序代码：

#include <cstdio>

int main( void )
{
    struct tree
    {
        int size;
        char values[27];
    };
    struct tree trees[27] = { 0 };

    for( int c, level=-1; c=getchar(), c!=EOF && c!='\n'; )
    {
        switch( c )
        {
        case '(': ++level; break;
        case ')': --level; break;
        case ' ': break;
        case ',': break;
        default: trees[level].values[ trees[level].size++ ] = c;
        }
    }

    for( size_t level=0; level!=27 && trees[level].size!=0; ++level )
        printf( "%.*s", trees[level].size, trees[level].values );
    putchar( '\n' );

    return 0;
}