105 lines
2.6 KiB
Java
105 lines
2.6 KiB
Java
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//符合下列属性的数组 arr 称为 山脉数组 ：
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//
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// arr.length >= 3
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// 存在 i（0 < i < arr.length - 1）使得：
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//
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// arr[0] < arr[1] < ... arr[i-1] < arr[i]
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// arr[i] > arr[i+1] > ... > arr[arr.length - 1]
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//
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//
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//
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//
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// 给你由整数组成的山脉数组 arr ，返回任何满足 arr[0] < arr[1] < ... arr[i - 1] < arr[i] > arr[i +
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//1] > ... > arr[arr.length - 1] 的下标 i 。
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//
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//
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//
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// 示例 1：
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//
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//
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//输入：arr = [0,1,0]
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//输出：1
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//
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//
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// 示例 2：
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//
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//
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//输入：arr = [0,2,1,0]
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//输出：1
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//
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//
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// 示例 3：
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//
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//
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//输入：arr = [0,10,5,2]
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//输出：1
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//
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//
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// 示例 4：
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//
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//
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//输入：arr = [3,4,5,1]
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//输出：2
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//
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//
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// 示例 5：
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//
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//
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//输入：arr = [24,69,100,99,79,78,67,36,26,19]
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//输出：2
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//
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//
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//
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//
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// 提示：
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//
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//
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// 3 <= arr.length <= 104
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// 0 <= arr[i] <= 106
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// 题目数据保证 arr 是一个山脉数组
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//
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//
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//
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//
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// 进阶：很容易想到时间复杂度 O(n) 的解决方案，你可以设计一个 O(log(n)) 的解决方案吗？
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// Related Topics 二分查找
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// 👍 179 👎 0
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package leetcode.editor.cn;
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//852:山脉数组的峰顶索引
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public class PeakIndexInAMountainArray {
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public static void main(String[] args) {
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//测试代码
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Solution solution = new PeakIndexInAMountainArray().new Solution();
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System.out.println(solution.peakIndexInMountainArray(new int[]{0, 1, 0}));
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System.out.println(solution.peakIndexInMountainArray(new int[]{0, 2, 1, 0}));
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System.out.println(solution.peakIndexInMountainArray(new int[]{0, 10, 5, 2}));
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System.out.println(solution.peakIndexInMountainArray(new int[]{3, 4, 5, 1}));
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System.out.println(solution.peakIndexInMountainArray(new int[]{24, 69, 100, 99, 79, 78, 67, 36, 26, 19}));
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System.out.println(solution.peakIndexInMountainArray(new int[]{3,5,3,2,0}));
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}
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//力扣代码
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//leetcode submit region begin(Prohibit modification and deletion)
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class Solution {
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public int peakIndexInMountainArray(int[] arr) {
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int start = 0;
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int end = arr.length - 1;
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while (start < end) {
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int mid = start + (end - start) / 2;
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if (arr[mid - 1] < arr[mid] && arr[mid] > arr[mid + 1]) {
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return mid;
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}
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if (arr[mid - 1] > arr[mid]) {
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end = mid;
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} else {
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start = mid;
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}
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}
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return start;
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}
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}
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//leetcode submit region end(Prohibit modification and deletion)
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}
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