add code of 66

Author: Li Li

top-interview-questions/66. Plus One.cs

@@ -0,0 +1,17 @@
+// add from last digit
+public class Solution {
+    public int[] PlusOne(int[] digits) {
+        if (digits == null || digits.Length == 0) return null;
+        int n = digits.Length;
+        for (int i = n - 1; i >= 0; i--) {
+            if (digits[i] < 9) {
+                digits[i]++;
+                return digits;
+            }
+            digits[i] = 0;
+        }
+        int[] newDigits = new int[n + 1];
+        newDigits[0] = 1;
+        return newDigits;
+    }
+}