Returns length of LCS for X [ 0. . m - 1 ] , Y [ 0. . n - 1 ]
int lcs ( char * X , char * Y , int m , int n ) { if ( m == 0 n == 0 ) return 0 ; if ( X [ m - 1 ] == Y [ n - 1 ] ) return 1 + lcs ( X , Y , m - 1 , n - 1 ) ; else return max ( lcs ( X , Y , m , n - 1 ) , lcs ( X , Y , m - 1 , n ) ) ; }