Databases
StackOverflow2013
Postsdbo
POFinding the local min/max in a 1D-Array/Histogram
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POFinding the local min/max in a 1D-Array/Histogram
    primarykey
    data
    text
    <p>I'm trying to find the indices of all the local minima and maxima within an Array.</p> <p>Example:</p> <pre><code>int[] array = {5,4,3,3,3,3,3,2,2,2, 6,6,8,5,5,5,3,3,2,1, 1,4,4,7}; // | | | // Indices: 0,1,2,3,4,5,6,7,8,9, 10,1,2,3,4,5,6,7,8,9, 20,1,2,3 // Minima: 8, 20 // Maxima: 12 </code></pre> <p>I came up with an algorithm about which I have few questions:</p> <ul> <li>Is there a much better one? :)</li> <li>I used an Enum with methods to achieve this dualism that UP and STRAIGHT_UP are both "UP". Seems messy to me. Any suggestions?</li> <li>Do you have better method-names? direction() (+return value) kind of implies that STRAIGHT is not a dir. But at the same time it is, since its an element in the Emum. Hm.</li> <li>It works for the given array. Do you see a situation where it does not?</li> </ul> <p>-</p> <pre><code>import java.util.ArrayList; public class MinMaxFinder { private int[] array; private ArrayList&lt;Integer&gt; minima; private ArrayList&lt;Integer&gt; maxima; private enum Direction{ UP, DOWN, STRAIGHT_UP, STRAIGHT_DOWN, STRAIGHT; public Direction direction(){ if(this==UP || this==STRAIGHT_UP){ return UP; }else if(this==DOWN || this==STRAIGHT_DOWN){ return DOWN; }else{ return STRAIGHT; } } public boolean isStraight(){ if(this==STRAIGHT_DOWN || this==STRAIGHT_UP || this==STRAIGHT){ return true; }else{ return false; } } public boolean hasDifferentDirection(Direction other){ if(this!=STRAIGHT &amp;&amp; other!=STRAIGHT &amp;&amp; this.direction() != other.direction() ){ return true; } return false; } } public MinMaxFinder(int[] array){ this.array = array; } public void update() { minima = new ArrayList&lt;Integer&gt;(); maxima = new ArrayList&lt;Integer&gt;(); Direction segmentDir = Direction.DOWN; int indexOfDirectionChange = 0; int prevVal = array[0]; int arrayLength = array.length; for(int i=1; i&lt;arrayLength; i++){ int currVal = array[i]; Direction currentDir = currVal&lt;prevVal?Direction.DOWN:(currVal&gt;prevVal?Direction.UP:Direction.STRAIGHT); prevVal = currVal; if(currentDir.hasDifferentDirection(segmentDir)){ int changePos = (indexOfDirectionChange+i-1)/2; if(currentDir.direction() == Direction.DOWN){ maxima.add(changePos); }else{ minima.add(changePos); } segmentDir = currentDir; indexOfDirectionChange = i; }else if( currentDir.isStraight() ^ segmentDir.isStraight() ){ indexOfDirectionChange = i; if(currentDir.isStraight() &amp;&amp; segmentDir.direction()==Direction.UP){ segmentDir=Direction.STRAIGHT_UP; }else if(currentDir.isStraight() &amp;&amp; segmentDir.direction()==Direction.DOWN){ segmentDir=Direction.STRAIGHT_DOWN; }else{ segmentDir = currentDir; } } } } public ArrayList&lt;Integer&gt; getMinima() { return minima; } public ArrayList&lt;Integer&gt; getMaxima() { return maxima; } } </code></pre>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. This table or related slice is empty.
    1. USPhil
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POFinding the local min/max in a 1D-Array/Histogram
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POFinding the local min/max in a 1D-Array/Histogram
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. POFinding the local min/max in a 1D-Array/Histogram
      1. This table or related slice is empty.
      1. VTUpMod
    1. COWhy is index 0 (the number 5) not a local maximum? Same for index 23. Can the first/last numbers never be a maximum/minimum?
      singulars
      1. POFinding the local min/max in a 1D-Array/Histogram
      1. USDominik Sandjaja
    2. CODoes it matter, in case of repetition of values, which of the indexes you select?? E.g.: a={5,6,6,6}, must 'max' be 2 or it is ok for it 1,2 or 3??
      singulars
      1. POFinding the local min/max in a 1D-Array/Histogram
      1. USmdm
    3. COAlso, I agree with @DaDaDom: 7 (index 23) should be a maximum
      singulars
      1. POFinding the local min/max in a 1D-Array/Histogram
      1. USmdm
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload