equilibrium point function

EquilibriumIndex.php

@@ -1,9 +1,58 @@
 <?php
 
 # Put a valid docblock here!
+/** 
+* This function finds the equilibrium Index in an array
+* The equilibrium Index is one where the sum of elements to the left 
+* and the sum of elements to the right is equal
+* Note that the value of the element at this equilibrium index 
+* is NOT added on either side.
+* Based on the test case provided, the function returns a 2 element array:
+* First element is the equilibrium index, and second element is the count of elements 
+* not counting the equilibrium element
+* if not equilibrium is found, the function returns an empty array
+*/
 function getEquilibriums($arr) {
 	$output = array();
 	# Logic goes here!
-	return $output;
+
+	// get the number of elements in the array ..
+	$ecount = count($arr);
+    	if ($ecount <= 2) // we'll return an empty array if there aren't sufficient elements
+		return $output;
+
+	// thinking of the two sides - start keeping totals of left and right
+	// with two indexes of where each side is - and bring them together
+	$lIdx = 0; // start the left side as the first element
+	$lTot = $arr[$lIdx];
+
+	$rIdx = $ecount - 1;  // start the right side as the last element
+	$rTot = $arr[$rIdx];
+
+	while ($lIdx < ($rIdx - 2)) { 
+		// make sure there is an unused element that is potentially the fulcrum ..
+		// if the left total is <= right total, add the next available element on the left to the left total
+		// and move the left index right towards the equilibrium point if any
+        	if ($lTot <= $rTot) {
+			$lIdx++;
+			$lTot += $arr[$lIdx];
+		} else {
+		// else if the left total is > right total, 
+		// add the next available element on the right to the right total
+		// and move the right index towards the equlibrium point if any
+			if ($lTot > $rTot) { // redundant if stmt - for readability, remove for performance
+				$rIdx--;
+				$rTot += $arr[$rIdx];
+			}
+        	}
+    	}
+
+    	// we've come to a point where there's only one element bet our two converging indexes
+    	// verify that and see if the two sides have the same total
+    	if (($lIdx == ($rIdx - 2)) && ($rTot == $lTot)) {
+		$output[0] = $lIdx + 1; // if yes, return the element between the two indexes
+		$output[1] = $ecount - 1;
+	} else { // return an empty array
+		return $output; 
+	}
 }
-