add 1539

fishercoder1534 · fishercoder1534 · commit 03a832a38e59 · 2020-08-08T10:17:30.000-07:00
diff --git a/README.md b/README.md
@@ -8,6 +8,7 @@ _If you like this project, please leave me a star._ &#9733;
 
 |  #  |      Title     |   Solutions   | Video  | Difficulty  | Tag                   
 |-----|----------------|---------------|--------|-------------|-------------
+|1539|[Kth Missing Positive Number](https://leetcode.com/problems/kth-missing-positive-number/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1539.java) | |Medium|Array, HashTable|
 |1535|[Find the Winner of an Array Game](https://leetcode.com/problems/find-the-winner-of-an-array-game/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1535.java) | [:tv:](https://youtu.be/v6On1TQfMTU) |Medium|Array|
 |1534|[Count Good Triplets](https://leetcode.com/problems/count-good-triplets/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1534.java) | |Easy|Array|
 |1528|[Shuffle String](https://leetcode.com/problems/shuffle-string/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1528.java) | |Easy|Sort|
diff --git a/src/main/java/com/fishercoder/solutions/_1539.java b/src/main/java/com/fishercoder/solutions/_1539.java
@@ -0,0 +1,67 @@
+package com.fishercoder.solutions;
+
+import java.util.HashSet;
+import java.util.Set;
+
+public class _1539 {
+    public static class Solution1 {
+        /**
+         * Space: O(n)
+         * Time: O(n)
+         */
+        public int findKthPositive(int[] arr, int k) {
+            Set<Integer> set = new HashSet<>();
+            int max = 0;
+            for (int i : arr) {
+                set.add(i);
+                max = Math.max(max, i);
+            }
+            int missed = 0;
+            for (int i = 1; i <= max; i++) {
+                if (!set.contains(i)) {
+                    missed++;
+                }
+                if (missed == k) {
+                    return i;
+                }
+            }
+            while (missed++ < k) {
+                max++;
+            }
+            return max;
+        }
+    }
+
+    public static class Solution2 {
+        /**
+         * Space: O(1)
+         * Time: O(n)
+         */
+        public int findKthPositive(int[] arr, int k) {
+            int missed = 0;
+            for (int i = 0; i < arr.length; i++) {
+                if (i == 0) {
+                    missed += arr[0] - 1;
+                    if (missed >= k) {
+                        return k;
+                    }
+                } else {
+                    missed += arr[i] - arr[i - 1] - 1;
+                    if (missed >= k) {
+                        missed -= arr[i] - arr[i - 1] - 1;
+                        int result = arr[i - 1];
+                        while (missed++ < k) {
+                            result++;
+                        }
+                        return result;
+                    }
+                }
+            }
+            int result = arr[arr.length - 1];
+            while (missed++ < k) {
+                result++;
+            }
+            return result;
+        }
+    }
+}
diff --git a/src/test/java/com/fishercoder/_1539Test.java b/src/test/java/com/fishercoder/_1539Test.java
@@ -0,0 +1,44 @@
+package com.fishercoder;
+
+import com.fishercoder.solutions._1539;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static junit.framework.TestCase.assertEquals;
+
+public class _1539Test {
+    private static _1539.Solution1 solution1;
+    private static _1539.Solution2 solution2;
+    private static int[] arr;
+
+    @BeforeClass
+    public static void setup() {
+        solution1 = new _1539.Solution1();
+        solution2 = new _1539.Solution2();
+    }
+
+    @Test
+    public void test1() {
+        arr = new int[]{2, 3, 4, 7, 11};
+        assertEquals(9, solution1.findKthPositive(arr, 5));
+    }
+
+    @Test
+    public void test2() {
+        arr = new int[]{1, 2, 3, 4};
+        assertEquals(6, solution1.findKthPositive(arr, 2));
+    }
+
+    @Test
+    public void test3() {
+        arr = new int[]{2, 3, 4, 7, 11};
+        assertEquals(9, solution2.findKthPositive(arr, 5));
+    }
+
+    @Test
+    public void test4() {
+        arr = new int[]{1, 2, 3, 4};
+        assertEquals(6, solution2.findKthPositive(arr, 2));
+    }
+
+}
