add solution of problem 386: lexicographical numbers

Author: ppulse

LexicographicalNumbers386/README.md

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+Given an integer *n*, return 1 - *n* in lexicographical order.
+
+For example, given 13, return: [1,10,11,12,13,2,3,4,5,6,7,8,9].
+
+Please optimize your algorithm to use less time and space. The input size may be as large as 5,000,000.

LexicographicalNumbers386/Solution.java

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+public class Solution {
+    public List<Integer> lexicalOrder(int n) {
+        List<Integer> result = new ArrayList<Integer>();
+        if (n <= 0)
+            return result;
+        
+        Stack<Integer> stack = new Stack();
+        stack.push(1);
+        
+        while (!stack.empty()) {
+            int value = stack.pop();
+            
+            while (value <= n) {
+                if (value%10 <= 8 && value+1 <= n)
+                    stack.push(value + 1);
+                    
+                result.add(value);
+                value *= 10;
+            }
+        }
+        
+        return result;
+    }
+}