add 1991

fishercoder1534 · fishercoder1534 · commit b614e8d05cb4 · 2021-09-04T09:17:17.000-07:00
diff --git a/README.md b/README.md
@@ -8,6 +8,8 @@ _If you like this project, please leave me a star._ &#9733;
 
 |  #  |      Title     |   Solutions   | Video  | Difficulty  | Tag                  
 |-----|----------------|---------------|--------|-------------|-------------
+|1992|[Find All Groups of Farmland](https://leetcode.com/problems/find-all-groups-of-farmland/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1992.java) ||Medium||
+|1991|[Find the Middle Index in Array](https://leetcode.com/problems/find-the-middle-index-in-array/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1991.java) ||Easy||
 |1985|[Find the Kth Largest Integer in the Array](https://leetcode.com/problems/find-the-kth-largest-integer-in-the-array/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1985.java) ||Medium||
 |1984|[Minimum Difference Between Highest and Lowest of K Scores](https://leetcode.com/problems/minimum-difference-between-highest-and-lowest-of-k-scores/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1984.java) ||Easy||
 |1981|[Minimize the Difference Between Target and Chosen Elements](https://leetcode.com/problems/minimize-the-difference-between-target-and-chosen-elements/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1981.java) ||Medium|DP|
diff --git a/src/main/java/com/fishercoder/solutions/_1991.java b/src/main/java/com/fishercoder/solutions/_1991.java
@@ -0,0 +1,24 @@
+package com.fishercoder.solutions;
+
+public class _1991 {
+    public static class Solution1 {
+        public int findMiddleIndex(int[] nums) {
+            int middleIndex = -1;
+            long sum = 0;
+            for (int i = 0; i < nums.length; i++) {
+                sum += nums[i];
+            }
+            long leftSum = 0;
+            for (int i = 0; i < nums.length; i++) {
+                sum -= nums[i];
+                if (i > 0) {
+                    leftSum += nums[i - 1];
+                }
+                if (sum == leftSum) {
+                    return i;
+                }
+            }
+            return middleIndex;
+        }
+    }
+}
diff --git a/src/test/java/com/fishercoder/_1991Test.java b/src/test/java/com/fishercoder/_1991Test.java
@@ -0,0 +1,22 @@
+package com.fishercoder;
+
+import com.fishercoder.solutions._1991;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class _1991Test {
+    private static _1991.Solution1 solution1;
+
+    @BeforeClass
+    public static void setup() {
+        solution1 = new _1991.Solution1();
+    }
+
+    @Test
+    public void test1() {
+        assertEquals(3, solution1.findMiddleIndex(new int[]{2, 3, -1, 8, 4}));
+    }
+
+}
