Recursive solution to count substrings with same first and last characters | Function to count substrings with same first and last characters ; base cases ; Driver Code
< ? php function countSubstrs ( $ str , $ i , $ j , $ n ) { if ( $ n == 1 ) return 1 ; if ( $ n <= 0 ) return 0 ; $ res = countSubstrs ( $ str , $ i + 1 , $ j , $ n - 1 ) + countSubstrs ( $ str , $ i , $ j - 1 , $ n - 1 ) - countSubstrs ( $ str , $ i + 1 , $ j - 1 , $ n - 2 ) ; if ( $ str [ $ i ] == $ str [ $ j ] ) $ res ++ ; return $ res ; } $ str = " abcab " ; $ n = strlen ( $ str ) ; echo ( countSubstrs ( $ str , 0 , $ n - 1 , $ n ) ) ; ? >