Create Arith Geo

Author: ratracegrad

Arith Geo

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+/***************************************************************************************
+*                                                                                      *
+*                  CODERBYTE BEGINNER CHALLENGE                                        *
+*                                                                                      *
+*  Arith Geo                                                                            *
+*  Using the JavaScript language, have the function ArithGeo(arr) take the array of    *
+*  numbers stored in arr and return the string "Arithmetic" if the sequence follows    *
+*  an arithmetic pattern or return "Geometric" if it follows a geometric pattern. If   *
+*  the sequence doesn't follow either pattern return -1. An arithmetic sequence is     *
+*  one where the difference between each of the numbers is consistent, where as in a   *
+*  geometric sequence, each term after the first is multiplied by some constant or     *
+*  common ratio. Arithmetic example: [2, 4, 6, 8] and Geometric                        *
+*  example: [2, 6, 18, 54]. Negative numbers may be entered as parameters, 0 will not  *
+*  be entered, and no array will contain all the same elements.                        *
+*                                                                                      *
+*  SOLUTION                                                                            *
+*  To check for arithmetic pattern, start by getting the difference between the first  *
+*  two number. Then loop thru array starting in position 2 and subtract the previous   *
+*  number. If the difference is equal to the initial difference then you have an       *
+*  arithmetic pattern so return arithmetic. Next repeat by getting initial difference  *
+*  by dividing the first and second numbers. Loop through array starting in position   *
+*  2 and compare the current number divided by previous number. If difference is       *
+*  equal to the initial number then you have a geometric pattern. Else return -1.      *
+*                                                                                      *
+*  Steps for solution                                                                  *
+*    1) set flags for both patterns to True                                            *
+*    2) Loop thru array starting in position 2 and compare difference between current  *
+*       number and the previous number to see if it is equal to initial difference     *
+*    3) If aritimetic pattern exists return arithmetic else check for geometric        *
+*    4) Get difference between second numvber divided by first number                  *
+*    5) Loop thru array starting in position 2 and compare difference between current  *
+*       number and the previous to see if it is equal to the intial difference         *
+*    6) If geometric pattern exists return geometric                                   *
+*    7) Else return -1                                                                 *
+*                                                                                      *
+***************************************************************************************/
+
+function ArithGeo(arr) { 
+
+  var arithFlag = true, geoFlag = true;
+  var diff = arr[1] - arr[0];
+  
+  for (var i = 2; i < arr.length; i++) {
+    if ((arr[i] - arr[i-1]) !== diff) {
+      arithFlag = false;
+    }
+  }
+  if (arithFlag) {
+    return "Arithmetic";
+  }
+  else { // check for geometric pattern
+    diff = arr[1] / arr[0];
+    for (var i = 2; i < arr.length; i++) {
+      if ((arr[i] / arr[i-1]) !== diff) { 
+        geoFlag = false;
+      }
+    }
+    if (geoFlag) {
+      return "Geometric";
+    }
+    else {
+      return "-1";
+    }
+  }
+  
+}