add 0910 smallest-range-ii

leetcode/0910-Smallest-Range-II/README.md

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+Given an array A of integers, for each integer A[i] we need to choose either x = -K or x = K, and add x to A[i] (only once).
+
+After this process, we have some array B.
+
+Return the smallest possible difference between the maximum value of B and the minimum value of B.
+
+ 
+
+Example 1:
+```
+Input: A = [1], K = 0
+Output: 0
+Explanation: B = [1]
+```
+Example 2:
+```
+Input: A = [0,10], K = 2
+Output: 6
+Explanation: B = [2,8]
+```
+Example 3:
+```
+Input: A = [1,3,6], K = 3
+Output: 3
+Explanation: B = [4,6,3]
+```
+ 
+
+Note:
+
+    1 <= A.length <= 10000
+    0 <= A[i] <= 10000
+    0 <= K <= 10000
+