coded + unit tested

Author: Ram swaroop

src/me/ramswaroop/arrays/NextLargerNumber.java

@@ -0,0 +1,84 @@
+package me.ramswaroop.arrays;
+
+import me.ramswaroop.arrays.sorting.QuickSort;
+
+/**
+ * Created by IntelliJ IDEA.
+ *
+ * @author: ramswaroop
+ * @date: 10/30/15
+ * @time: 11:01 AM
+ */
+public class NextLargerNumber {
+
+    /**
+     * Finds the closest number which is larger
+     * than {@param n} by using only those digits
+     * present in {@param n} and using any digit
+     * only once.
+     *
+     * @param n
+     * @return
+     */
+    public static int findNextLargerNumber(Integer n) {
+
+        String str = n.toString();
+        int len = str.length();
+        int[] a = new int[len];
+        int minIndex;
+
+        // construct int array containing all 
+        // digits in number {@param n}  
+        for (int i = 0; i < len; i++) {
+            a[i] = Integer.parseInt(str.charAt(i) + "");
+        }
+
+        int i = len - 1;
+        while (i > 0) {
+            if (a[i] > a[i - 1]) break;
+            i--;
+        }
+
+        if (i <= 0) return -1;
+        
+        minIndex = i;
+        int j = len - 1;
+        while (j >= i) {
+            if (a[j] < a[minIndex] && a[j] > a[i - 1]) {
+                minIndex = j;
+            }
+            j--;
+        }
+
+        swap(a, i - 1, minIndex);
+
+        QuickSort.quickSort(a, i, len - 1);
+
+        StringBuilder builder = new StringBuilder();
+        for (int k = 0; k < len; k++) {
+            builder.append(a[k]);
+        }
+
+        return Integer.parseInt(builder.toString());
+    }
+
+    /**
+     * Swaps variables in {@param a} at {@param index1} with {@param index2}.
+     *
+     * @param a
+     * @param index1
+     * @param index2
+     */
+    private static void swap(int[] a, int index1, int index2) {
+        int temp = a[index1];
+        a[index1] = a[index2];
+        a[index2] = temp;
+    }
+
+    public static void main(String a[]) {
+        System.out.println(findNextLargerNumber(56));
+        System.out.println(findNextLargerNumber(65));
+        System.out.println(findNextLargerNumber(3451));
+        System.out.println(findNextLargerNumber(534976));
+    }
+}