How to replace the content of largest rectangle in histogram

Question

Can you please tell me, how can I replace the X with O, where the largest rectangle in the histogram is?

Here is my code to generate a histogram:

    public static void histogram() {

    double[] data1 = { 4.1, 6.2, 4.5, 8.0, 7.1, 6.2, 6.3, 0.1, 4.5, 5.1 };

    for (int columns = data1.length; columns >= 1; columns--) {
        for (int zeilen = 0; zeilen < data1.length; zeilen++) {
            if (data1[zeilen] >= columns) {
                System.out.print("X");
            } else {
                System.out.print(" ");
            }
        }
        System.out.println();
    }
}

public static void main(String[] args) {
    histogram();
}

The output should be roughly like this:

   X      
   XX     
 X OOOO   
 X OOOO  X
XXXOOOO XX
XXXOOOO XX
XXXOOOO XX
XXXOOOO XX

OR like this:

   X      
   XX     
 X XXXX   
 X XXXX  X
OOOOOOO XX
OOOOOOO XX
OOOOOOO XX
OOOOOOO XX

Just where die largest field is.

Answer 1

The simplest way to do is to find the max value in your array first.

int max=0;
for (int i = 0; i < data1.length; i++) {
    if (data1[i] > max)
        max = data1[i];
}

Then in your loop, check if the data you are working with equals to the maximum value, and use "O" to display.

if (data1[zeilen] == max)
    System.out.println("O");
else
    System.out.println("X");

Then your maximum rectangle will be with "O" .

Answer 2

One way would be to determine which index value in the array holds the largest element. You could do this using a loop or streams:

int maxIndex = IntStream.range(0, data1.length)
    .reduce((i1, i2) -> data1[i1] > data1[i2] ? i1 : i2)
    .orElseGet(() -> 0); // If only one element, max must be first

Then when printing out the histogram you can select the character to output based on whether the indexes match.

for (int columns = data1.length; columns >= 1; columns--) {
  for (int zeilen = 0; zeilen < data1.length; zeilen++) {
    if (data1[zeilen] >= columns) {
      System.out.print(zeilen == maxIndex ? 'O' : 'X');
    } else {
      System.out.print(" ");
    }
  }
  System.out.println();
}

I'm not sure that your range for columns in the first loop (from data1.length down to 1 ) is a great choice. From (int)data1[maxIndex] down to 1 might be better.

---

OK, the edit makes it a more interesting problem. The simplest way to solve this may be by recursive subdivision:

1. For range [start, end) , find the histogram index with the minimum value, index . This can be calculated similarly to the max index value code above.

2. Repeat step 1 for [start, index) recursively if start < index .

3. Repeat step 1 for [index + 1, end) recursively if index + 1 < end .

4. Return the rectangle with maximum area from steps 1, 2 and 3.