add 852 java

Author: yennanliu

.github/workflows/maven.yml

@@ -1,35 +1,35 @@
-# This workflow will build a Java project with Maven, and cache/restore any dependencies to improve the workflow execution time
-# For more information see: https://docs.github.com/en/actions/automating-builds-and-tests/building-and-testing-java-with-maven
+# # This workflow will build a Java project with Maven, and cache/restore any dependencies to improve the workflow execution time
+# # For more information see: https://docs.github.com/en/actions/automating-builds-and-tests/building-and-testing-java-with-maven
 
-# This workflow uses actions that are not certified by GitHub.
-# They are provided by a third-party and are governed by
-# separate terms of service, privacy policy, and support
-# documentation.
+# # This workflow uses actions that are not certified by GitHub.
+# # They are provided by a third-party and are governed by
+# # separate terms of service, privacy policy, and support
+# # documentation.
 
-name: Java CI with Maven
+# name: Java CI with Maven
 
-on:
-  push:
-    branches: [ "master" ]
-  pull_request:
-    branches: [ "master" ]
+# on:
+#   push:
+#     branches: [ "master" ]
+#   pull_request:
+#     branches: [ "master" ]
 
-jobs:
-  build:
+# jobs:
+#   build:
 
-    runs-on: ubuntu-latest
+#     runs-on: ubuntu-latest
 
-    steps:
-    - uses: actions/checkout@v4
-    - name: Set up JDK 17
-      uses: actions/setup-java@v4
-      with:
-        java-version: '17'
-        distribution: 'temurin'
-        cache: maven
-    - name: Build with Maven
-      run:  cd leetcode_java && mvn package #cd leetcode_java && mvn -B package --file pom.xml
+#     steps:
+#     - uses: actions/checkout@v4
+#     - name: Set up JDK 17
+#       uses: actions/setup-java@v4
+#       with:
+#         java-version: '17'
+#         distribution: 'temurin'
+#         cache: maven
+#     - name: Build with Maven
+#       run:  cd leetcode_java && mvn package #cd leetcode_java && mvn -B package --file pom.xml
 
-    # Optional: Uploads the full dependency graph to GitHub to improve the quality of Dependabot alerts this repository can receive
-    - name: Update dependency graph
-      uses: advanced-security/maven-dependency-submission-action@571e99aab1055c2e71a1e2309b9691de18d6b7d6
+#     # Optional: Uploads the full dependency graph to GitHub to improve the quality of Dependabot alerts this repository can receive
+#     - name: Update dependency graph
+#       uses: advanced-security/maven-dependency-submission-action@571e99aab1055c2e71a1e2309b9691de18d6b7d6

README.md

@@ -877,7 +877,7 @@
 540|[Single Element in a Sorted Array](https://leetcode.com/problems/dsingle-element-in-a-sorted-array/)| [Python](./leetcode_python/Binary_Search/single-element-in-a-sorted-array.py) | _O(logn)_ | _O(1)_ | Medium | | OK* 
 658 | [Find K Closest Elements](https://leetcode.com/problems/find-k-closest-elements/) | [Python](./leetcode_python/Binary_Search/find-k-closest-elements.py) | _O(logn + k)_ | _O(1)_ | Medium |`good trick`, sorting, stack, `two pointers`,`binary search`,`amazon`,`fb`, google| AGAIN ************** (5) (MUST) 
 744 | [Find Smallest Letter Greater Than Target](https://leetcode.com/problems/find-smallest-letter-greater-than-target/) | [Python](./leetcode_python/Binary_Search/find-smallest-letter-greater-than-target.py) | _O(logn)_ | _O(1)_ | Easy | | OK* 
-852 | [Peak Index in a Mountain Array](https://leetcode.com/problems/peak-index-in-a-mountain-array/) | [Python](./leetcode_python/Binary_Search/peak-index-in-a-mountain-array.py) | _O(logn)_ | _O(1)_ | Medium | LC 162 Find Peak Element, `amazon`| OK* (2)
+852 | [Peak Index in a Mountain Array](https://leetcode.com/problems/peak-index-in-a-mountain-array/) | [Python](./leetcode_python/Binary_Search/peak-index-in-a-mountain-array.py), [Java](./leetcode_java/src/main/java/LeetCodeJava/BinarySearch/PeakIndexInAMountainArray.java) | _O(logn)_ | _O(1)_ | Medium | LC 162 Find Peak Element, `amazon`, google| OK* (2)
 875 | [Koko Eating Bananas](https://leetcode.com/problems/koko-eating-bananas/) | [Python](./leetcode_python/Binary_Search/koko-eating-bananas.py), [Java](./leetcode_java/src/main/java/LeetCodeJava/BinarySearch/KokoEatingBananas.java) | _O(nlogr)_ | _O(1)_ | Medium | binary search, left boundary, good basic| AGAIN******* (4)(MUST)
 894| [All Possible Full Binary Trees](https://leetcode.com/problems/all-possible-full-binary-trees/) | [Python](./leetcode_python/Binary_Search/all-possible-full-binary-trees.py) | _O(n * 4^n / n^(3/2))_ | _O(n * 4^n / n^(3/2))_ | Medium ||  AGAIN (not start)
 911| [Online Election](https://leetcode.com/problems/online-election/) |  [Python](./leetcode_python/Binary_Search/online-election.py)| ctor: _O(n)_<br> query : _O(logn)_ | _O(n)_ | Medium    ||   AGAIN (not start)

leetcode_java/src/main/java/LeetCodeJava/BinarySearch/PeakIndexInAMountainArray.java

@@ -0,0 +1,69 @@
+package LeetCodeJava.BinarySearch;
+
+// https://leetcode.com/problems/peak-index-in-a-mountain-array/description/
+// https://leetcode.cn/problems/peak-index-in-a-mountain-array/description/
+/**
+ * 852. Peak Index in a Mountain Array
+ * Solved
+ * Medium
+ * Topics
+ * Companies
+ * You are given an integer mountain array arr of length n where the values increase to a peak element and then decrease.
+ *
+ * Return the index of the peak element.
+ *
+ * Your task is to solve it in O(log(n)) time complexity.
+ *
+ *
+ *
+ * Example 1:
+ *
+ * Input: arr = [0,1,0]
+ *
+ * Output: 1
+ *
+ * Example 2:
+ *
+ * Input: arr = [0,2,1,0]
+ *
+ * Output: 1
+ *
+ * Example 3:
+ *
+ * Input: arr = [0,10,5,2]
+ *
+ * Output: 1
+ *
+ *
+ *
+ * Constraints:
+ *
+ * 3 <= arr.length <= 105
+ * 0 <= arr[i] <= 106
+ * arr is guaranteed to be a mountain array.
+ * Seen this question in a real interview before?
+ * 1/5
+ * Yes
+ * No
+ * Accepted
+ * 928.3K
+ * Submissions
+ * 1.4M
+ * Acceptance Rate
+ * 67.9%
+ * Topics
+ * Companies
+ * Similar Questions
+ * Discussion (183)
+ *
+ *
+ */
+public class PeakIndexInAMountainArray {
+
+    // V0
+//    public int peakIndexInMountainArray(int[] arr) {
+//
+//    }
+    // V1
+    // V2
+}

leetcode_java/src/main/java/dev/workspace6.java

@@ -2244,4 +2244,76 @@ private boolean isStrobogrammatic(String x){
         return true;
     }
 
+    // LC 852
+    // https://leetcode.com/problems/peak-index-in-a-mountain-array/
+    /**
+     *
+     *
+     *  Example 1:
+     *
+     * Input: arr = [0,1,0]
+     *
+     * Output: 1
+     *
+     * Example 2:
+     *
+     * Input: arr = [0,2,1,0]
+     *
+     * Output: 1
+     *
+     * Example 3:
+     *
+     * Input: arr = [0,10,5,2]
+     *
+     * Output: 1
+     *
+     * Exp 1 : [0,3,2,1,0] -> 1
+     *
+     * IDEA: BINARY SEARCH
+     *
+     * -> if there is a peak at index i
+     * then 0 - i-1 MUST be increasing
+     *
+     */
+    public int peakIndexInMountainArray(int[] arr) {
+
+        // edge
+        int maxIdx = -1;
+        int maxVal = -1;
+        if (arr.length == 3){
+            for(int i = 0; i < arr.length; i++){
+                if(arr[i] > maxVal){
+                    maxVal = arr[i];
+                    maxIdx = i;
+                }
+            }
+            return maxIdx;
+        }
+
+        // binary search
+        int l = 0;
+        int r = arr.length - 1;
+        while (r >= l){
+            int mid = (l + r) / 2;
+
+            // case 1)  cur > left and cur > right (find peak)
+            if (arr[mid] > arr[mid-1] && arr[mid] > arr[mid+1]){
+                return mid;
+            }
+            // Exp 1 : [0,0,0, 3,2,1,0] -> 1
+            // case 2) cur < left && cur > left most
+            else if (arr[mid] < arr[mid-1] && arr[mid] >= arr[l]){
+                l = mid + 1;
+            }
+            // case 3) cur < right and cur > right most
+            else if  (arr[mid] < arr[mid-1] && arr[mid] >= arr[r]){
+                r = mid - 1;
+        }
+
+        return 0;
+    }
+
+        return -1;
+    }
+
 }