add 775

fishercoder1534 · fishercoder1534 · commit 43ccd93a232f · 2021-04-05T08:24:38.000-07:00
diff --git a/README.md b/README.md
@@ -467,6 +467,7 @@ _If you like this project, please leave me a star._ &#9733;
 |781|[Rabbits in Forest](https://leetcode.com/problems/rabbits-in-forest/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_781.java) | [:tv:](https://youtu.be/leiSa1i-QrI) |Medium| HashTable, Math
 |779|[K-th Symbol in Grammar](https://leetcode.com/problems/k-th-symbol-in-grammar/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_779.java) |  |Medium|
 |776|[Split BST](https://leetcode.com/problems/split-bst/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_776.java) | |Medium| Recursion
+|775|[Global and Local Inversions](https://leetcode.com/problems/global-and-local-inversions/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_775.java) | |Medium| Array, Math
 |771|[Jewels and Stones](https://leetcode.com/problems/jewels-and-stones/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_771.java) |  |Easy|
 |769|[Max Chunks To Make Sorted](https://leetcode.com/problems/max-chunks-to-make-sorted/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_769.java) |  |Medium| Array
 |767|[Reorganize String](https://leetcode.com/problems/reorganize-string/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_767.java) | |Medium|
diff --git a/src/main/java/com/fishercoder/solutions/_775.java b/src/main/java/com/fishercoder/solutions/_775.java
@@ -0,0 +1,46 @@
+package com.fishercoder.solutions;
+
+public class _775 {
+    /**
+     * credit: https://leetcode.com/problems/global-and-local-inversions/solution/
+     */
+    public static class Solution1 {
+        /**
+         * 1. a local inversion is also a global inversion;
+         * 2. we only need to check if a this input has any non-local inversion, i.e. global inversions that are not local inversions
+         * because local inversion is a subset of global inversions.
+         * <p>
+         * This one will result in TLE with a time complexity of O(n^2).
+         */
+        public boolean isIdealPermutation(int[] A) {
+            for (int i = 0; i < A.length; i++) {
+                for (int j = i + 2; j < A.length; j++) {
+                    if (A[i] > A[j]) {
+                        return false;
+                    }
+                }
+            }
+            return true;
+        }
+    }
+
+    public static class Solution2 {
+        /**
+         * from the above solution, we can tell that if we can find the minimum of A[j] where j >= i + 2, then we could quickly return false, so two steps:
+         * 1. remembering minimum
+         * 2. scanning from right to left
+         * <p>
+         * Time: O(n)
+         */
+        public boolean isIdealPermutation(int[] A) {
+            int min = A.length;
+            for (int i = A.length - 1; i >= 2; i--) {
+                min = Math.min(min, A[i]);
+                if (A[i - 2] > min) {
+                    return false;
+                }
+            }
+            return true;
+        }
+    }
+}
diff --git a/src/test/java/com/fishercoder/_775Test.java b/src/test/java/com/fishercoder/_775Test.java
@@ -0,0 +1,22 @@
+package com.fishercoder;
+
+import com.fishercoder.solutions._775;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class _775Test {
+    private static _775.Solution1 solution1;
+
+    @BeforeClass
+    public static void setup() {
+        solution1 = new _775.Solution1();
+    }
+
+    @Test
+    public void test1() {
+        assertEquals(true, solution1.isIdealPermutation(new int[]{0, 1}));
+    }
+
+}
