static int countOfSubstringWithKOnes ( String s , int K ) {
  int N = s . length ( ) ;
  int res = 0 ;
  int countOfOne = 0 ;
  int [ ] freq = new int [ N + 1 ] ;
  freq [ 0 ] = 1 ;
  for ( int i = 0 ;
  i < N ;
  i ++ ) {
    countOfOne += ( s . charAt ( i ) - '0' ) ;
    if ( countOfOne >= K ) {
      res += freq [ countOfOne - K ] ;
    }
    freq [ countOfOne ] ++ ;
  }
  return res ;
}

static int countOfSubstringWithKOnes ( String s , int K ) { int N = s . length ( ) ; int res = 0 ; int countOfOne = 0 ; int [ ] freq = new int [ N + 1 ] ; freq [ 0 ] = 1 ; for ( int i = 0 ; i < N ; i ++ ) { countOfOne += ( s . charAt ( i ) - '0' ) ; if ( countOfOne >= K ) { res += freq [ countOfOne - K ] ; } freq [ countOfOne ] ++ ; } return res ; }
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