Create 0034-find-first-and-last-position-of-element-in-sorted-array.js

Solved find-first-and-last-position-of-element-in-sorted-array in js.

javascript/0034-find-first-and-last-position-of-element-in-sorted-array.js

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+/**
+ * Binary Search
+ * https://leetcode.com/problems/find-first-and-last-position-of-element-in-sorted-array/
+ * Time O(log(n)) | Space O(1)
+ * @param {number[]} nums
+ * @param {number} target
+ * @return {number[]}
+ */
+var searchRange = function(nums, target) {
+
+    const result = [];
+
+    result.push(binarySearch(true));
+    result.push(binarySearch(false));
+
+    function binarySearch(leftBias) {
+      let left = 0;
+      let right = nums.length - 1;
+      let index = -1;
+
+      while(left <= right) {
+
+        const mid = Math.floor((left+right)/2);
+
+        if(target > nums[mid]) {
+          left = mid+1;
+        }
+        if(target < nums[mid]) {
+          right = mid-1;
+        }
+        // this is the meat of the code
+        if(target === nums[mid]) {
+          if(leftBias) {
+            index = mid;
+            right = mid - 1;
+          } else {
+            index = mid;
+            left = mid + 1;
+          }
+        }
+      }
+
+      return index;
+    }
+
+    return result;
+};