For a particular value of i and j , len [ currRow ] [ j ] stores length of longest common substring in string X [ 0. . i ] and Y [ 0. . j ] .
for ( int i = 0 ; i < m ; i ++ ) { for ( int j = 0 ; j < n ; j ++ ) { if ( i == 0 j == 0 ) { len [ currRow ] [ j ] = 0 ; } else if ( X . charAt ( i - 1 ) == Y . charAt ( j - 1 ) ) { len [ currRow ] [ j ] = len [ ( 1 - currRow ) ] [ ( j - 1 ) ] + 1 ; result = Math . max ( result , len [ currRow ] [ j ] ) ; } else { len [ currRow ] [ j ] = 0 ; } }