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Rooted by: Find Peak Element
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  • Code 
    import java.util.*;;

class Solution {
  public static int peakIndex(int[] nums) {
    if (nums.length == 1) return 0;
    if (nums.length == 2) return nums[0] > nums[1] ? 0 : 1;
    
    boolean ascending = false;
    
    for (int i = 0; i < nums.length - 1; ++i) {
      if (nums[i] < nums[i + 1]) {
        ascending = true;
      } else {
        if (ascending && nums[i] > nums[i + 1]) {
          return i;
        }
        ascending = false;
      }
    }
    
    if (ascending) {
      return nums.length - 1;
    } else {
      return -1;
    }
  }
}
     Test Cases 
    import org.junit.Test;
import static org.junit.Assert.assertEquals;
import org.junit.runners.JUnit4;

// TODO: Replace examples and use TDD development by writing your own tests

public class SolutionTest {
    @Test
    public void test1() {
        assertEquals(2, Solution.peakIndex(new int[] {1, 2, 3, 1}));
    }
    
    @Test
    public void test2() {
        assertEquals(1, Solution.peakIndex(new int[] {1, 2, 1}));
    }
    
    @Test
    public void test3() {
        assertEquals(0, Solution.peakIndex(new int[] {2}));
    }
    
    @Test
    public void test4() {
        assertEquals(4, Solution.peakIndex(new int[] {1, 2, 3, 4, 5, 4, 3, 2}));
    }
    
    @Test
    public void peakIsTheLastNumber() {
        assertEquals(4, Solution.peakIndex(new int[] {1, 2, 3, 4, 5}));
    }
    
    @Test
    public void flatland() {
        assertEquals(-1, Solution.peakIndex(new int[] {1, 1, 1, 1, 1}));
    }
}
    View Run Output
  • Code
    • import java.util.*;;
    • class Solution {
    • public static int peakIndex(int[] nums) {
    • int left = 0;
    • int right = nums.length - 1;
    • int peak = -1;
    • if (nums.length == 1) return 0;
    • if (nums.length == 2) return nums[0] > nums[1] ? 0 : 1;
    • while(left <= right) {
    • if(left == right) {
    • peak = left;
    • break;
    • }
    • int mid = (left + right) / 2;
    • if(nums[mid] < nums[mid + 1]) {
    • left = mid + 1;
    • boolean ascending = false;
    • for (int i = 0; i < nums.length - 1; ++i) {
    • if (nums[i] < nums[i + 1]) {
    • ascending = true;
    • } else {
    • right = mid;
    • if (ascending && nums[i] > nums[i + 1]) {
    • return i;
    • }
    • ascending = false;
    • }
    • }
    • return peak;
    • if (ascending) {
    • return nums.length - 1;
    • } else {
    • return -1;
    • }
    • }
    • }
     Test Cases
    • import org.junit.Test;
    • import static org.junit.Assert.assertEquals;
    • import org.junit.runners.JUnit4;
    • // TODO: Replace examples and use TDD development by writing your own tests
    • public class SolutionTest {
    • @Test
    • public void test1() {
    • assertEquals(2, Solution.peakIndex(new int[] {1, 2, 3, 1}));
    • }
    • @Test
    • public void test2() {
    • assertEquals(1, Solution.peakIndex(new int[] {1, 2, 1}));
    • }
    • @Test
    • public void test3() {
    • assertEquals(0, Solution.peakIndex(new int[] {2}));
    • }
    • @Test
    • public void test4() {
    • assertEquals(4, Solution.peakIndex(new int[] {1, 2, 3, 4, 5, 4, 3, 2}));
    • }
    • @Test
    • public void test5() {
    • assertEquals(14, Solution.peakIndex(new int[] {1, 2, 3, 2, 1, 2, 3, 4, 5, 4, 3, 4, 5, 6, 7, 6, 5, 4, 3, 7, 8, 1}));
    • public void peakIsTheLastNumber() {
    • assertEquals(4, Solution.peakIndex(new int[] {1, 2, 3, 4, 5}));
    • }
    • @Test
    • public void flatland() {
    • assertEquals(-1, Solution.peakIndex(new int[] {1, 1, 1, 1, 1}));
    • }
    • }