add: Search for a Range

Author: hijiangtao

README.md

@@ -13,6 +13,7 @@ Progress: 20/
 |19|[Remove Nth Node From End of List](https://leetcode.com/problems/remove-nth-node-from-end-of-list/) | [JavaScript](./src/remove-nth-node-from-end-of-list/res.js)|Medium|
 |22|[Generate Parentheses](https://leetcode.com/problems/generate-parentheses/) | [JavaScript](./src/generate-parentheses/res.js)|Medium|
 |26|[Remove Duplicates from Sorted Array](https://leetcode.com/problems/remove-duplicates-from-sorted-array/) | [JavaScript](./src/remove-duplicates-from-sorted-array/res.js)|Easy|
+|34|[Search for a Range](https://leetcode.com/problems/search-for-a-range/) | [JavaScript](./src/search-for-a-range/res.js)|Medium|
 |48|[Rotate Image](https://leetcode.com/problems/rotate-image/) | [JavaScript](./src/rotate-image/res.js)|Medium|
 |66|[Plus One](https://leetcode.com/problems/plus-one/) | [JavaScript](./src/plus-one/res.js)|Easy|
 |69|[Sqrt(x)](https://leetcode.com/problems/sqrtx/) | [JavaScript](./src/sqrtx/res.js)|Easy|

src/search-for-a-range/res.js

@@ -0,0 +1,68 @@
+// Given an array of integers sorted in ascending order, find the starting and ending position of a given target value.
+
+// Your algorithm's runtime complexity must be in the order of O(log n).
+
+// If the target is not found in the array, return [-1, -1].
+
+// For example,
+// Given [5, 7, 7, 8, 8, 10] and target value 8,
+// return [3, 4].
+
+/**
+ * res.js
+ * @authors Joe Jiang ([email protected])
+ * @date    2017-02-26 22:56:22
+ * @version $Id$
+ * 
+ * @param {number[]} nums
+ * @param {number} target
+ * @return {number[]}
+ */
+let searchRange = function(nums, target) {
+    let arrlen = nums.length;
+    if (!arrlen) {
+        return [-1, -1];
+    }
+    
+    let leftIndex = binarySearch(nums, 0, arrlen-1, target, 'l'), rightIndex;
+    if (leftIndex === -1) {
+        return [-1, -1];
+    } else {
+        rightIndex = binarySearch(nums, leftIndex, arrlen-1, target, 'r');
+    }
+    
+    return [leftIndex, rightIndex];
+};
+
+let binarySearch = function(nums, begin, end, target, type) {
+    let arrlen = nums.length;
+    while (begin <= end) {
+        let mid = begin + Number.parseInt( (end-begin)/2 ),
+            midVal = nums[mid];
+        
+        if (midVal === target) {
+            switch (type) {
+                case 'l':
+                    if (mid === 0 || nums[mid-1] !== target) {
+                        return mid;
+                    } else {
+                        end = mid-1;
+                    }
+                    break;
+                default:
+                    if (mid === arrlen-1 || nums[mid+1] !== target) {
+                        return mid;
+                    } else {
+                        begin = mid+1;
+                    }
+                    break;
+            }
+        } else if (midVal > target) {
+            end = mid-1;
+        } else if (midVal < target) {
+            begin = mid+1;
+        }
+    }
+    
+    return -1;
+};