static int findLength ( String str , int n ) {
  int sum [ ] = new int [ n + 1 ] ;
  sum [ 0 ] = 0 ;
  for ( int i = 1 ;
  i <= n ;
  i ++ ) sum [ i ] = ( sum [ i - 1 ] + str . charAt ( i - 1 ) - '0' ) ;
  int ans = 0 ;
  for ( int len = 2 ;
  len <= n ;
  len += 2 ) {
    for ( int i = 0 ;
    i <= n - len ;
    i ++ ) {
      int j = i + len - 1 ;
      if ( sum [ i + len / 2 ] - sum [ i ] == sum [ i + len ] - sum [ i + len / 2 ] ) ans = Math . max ( ans , len ) ;
    }
  }
  return ans ;
}

static int findLength ( String str , int n ) { int sum [ ] = new int [ n + 1 ] ; sum [ 0 ] = 0 ; for ( int i = 1 ; i <= n ; i ++ ) sum [ i ] = ( sum [ i - 1 ] + str . charAt ( i - 1 ) - '0' ) ; int ans = 0 ; for ( int len = 2 ; len <= n ; len += 2 ) { for ( int i = 0 ; i <= n - len ; i ++ ) { int j = i + len - 1 ; if ( sum [ i + len / 2 ] - sum [ i ] == sum [ i + len ] - sum [ i + len / 2 ] ) ans = Math . max ( ans , len ) ; } } return ans ; }
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