k th min element quick select O(n)

num exists in array and num does not exist
both cases covered

Author: dheeraj9198

src/Array/ExactlyXelemGreaterThanX.java

@@ -0,0 +1,78 @@
+package Array;
+
+/**
+ * Created by dheeraj on 7/17/2016.
+ * 1 2 3 5 7 9
+ * ans 3
+ * <p>
+ * 1- sort and do O(NlogN)
+ * 2- counting sort O(MaxElemValue)
+ * 3- quick select O(N)
+ */
+public class ExactlyXelemGreaterThanX {
+
+    //num exists in array
+/*    private static int getXContains(int[] ints) {
+        int start = 0;
+        int end = ints.length - 1;
+        int part = partition(ints, start, end);
+        while (part != -1 && ints[part] != ints.length-1 - part ) {
+            if (ints[part] > ints.length-1 - part) {
+                end = part - 1;
+                part = partition(ints, start, end);
+            } else {
+                start = part + 1;
+                part = partition(ints, start, end);
+            }
+        }
+        return part == -1 ? -1 : ints[part];
+    }*/
+
+    //array does not contain that number
+    private static int getXNotContains(int[] ints) {
+        int start = 0;
+        int end = ints.length - 1;
+        int part = partition(ints, start, end);
+        while (part != -1 && part + 1 != ints.length - 1 - part) {
+            if (ints[part] > ints.length - 1 - part) {
+                end = part - 1;
+                part = partition(ints, start, end);
+            } else {
+                start = part + 1;
+                part = partition(ints, start, end);
+            }
+        }
+        return part == -1 ? -1 : part + 1;
+    }
+
+    private static int partition(int[] array, int start, int end) {
+        if (start > end) {
+            return -1;
+        }
+        int pivot = array[end];
+        int index = start;
+
+        int temp;
+        for (int a = start; a < end; a++) {
+            if (array[a] < pivot) {
+                temp = array[index];
+                array[index] = array[a];
+                array[a] = temp;
+                index++;
+            }
+        }
+        temp = array[index];
+        array[index] = pivot;
+        array[end] = temp;
+        return index;
+    }
+
+    public static void main(String[] strings) {
+/*
+        int[] ints = new int[]{3, 1, 2, 7, 9, 5};
+*/
+        int[] ints = new int[]{0, 1, 2, 7, 9, 5};
+        System.out.println(getXNotContains(ints));
+    }
+
+}

src/Array/KthMinElementQuickSelect.java

@@ -7,17 +7,20 @@ public class KthMinElementQuickSelect {
 
     private static int getKthMin(int k, int[] ints) {
         int part = partition(ints, 0, ints.length - 1);
-        while (part != k-1) {
-            if (part > k-1) {
+        while (part != k - 1) {
+            if (part > k - 1) {
                 part = partition(ints, 0, part - 1);
             } else {
                 part = partition(ints, part + 1, ints.length - 1);
             }
         }
-        return ints[part];
+        return part == -1 ? -1 : ints[part];
     }
 
     private static int partition(int[] array, int start, int end) {
+        if (start > end) {
+            return -1;
+        }
         int pivot = array[end];
         int index = start;