1095. Find in Mountain Array

[Tcdian]

1095. Find in Mountain Array

（这是一个 交互式问题 ）

给你一个 山脉数组 mountainArr，请你返回能够使得 mountainArr.get(index) 等于 target 最小 的下标 index 值。

如果不存在这样的下标 index，就请返回 -1。

 

何为山脉数组？如果数组 A 是一个山脉数组的话，那它满足如下条件：

首先，A.length >= 3

其次，在 0 < i < A.length - 1 条件下，存在 i 使得：

A[0] < A[1] < ... A[i-1] < A[i]
A[i] > A[i+1] > ... > A[A.length - 1]
 

你将 不能直接访问该山脉数组，必须通过 MountainArray 接口来获取数据：

MountainArray.get(k) - 会返回数组中索引为k 的元素（下标从 0 开始）
MountainArray.length() - 会返回该数组的长度
 

注意：

对 MountainArray.get 发起超过 100 次调用的提交将被视为错误答案。此外，任何试图规避判题系统的解决方案都将会导致比赛资格被取消。

为了帮助大家更好地理解交互式问题，我们准备了一个样例 “答案”：https://leetcode-cn.com/playground/RKhe3ave，请注意这 不是一个正确答案。

Example 1

Input: array = [1,2,3,4,5,3,1], target = 3
Output: 2
Explanation: 3 exists in the array, at index=2 and index=5. Return the minimum index, which is 2.

Example 2

Input: array = [0,1,2,4,2,1], target = 3
Output: -1
Explanation: 3 does not exist in the array, so we return -1.

Note

• 3 <= mountain_arr.length() <= 10000
• 0 <= target <= 10^9
• 0 <= mountain_arr.get(index) <= 10^9

[Tcdian]

Solution

• JavaScript Solution

/**
 * // This is the MountainArray's API interface.
 * // You should not implement it, or speculate about its implementation
 * function MountainArray() {
 *     @param {number} index
 *     @return {number}
 *     this.get = function(index) {
 *         ...
 *     };
 *
 *     @return {number}
 *     this.length = function() {
 *         ...
 *     };
 * };
 */

/**
 * @param {number} target
 * @param {MountainArray} mountainArr
 * @return {number}
 */
var findInMountainArray = function(target, mountainArr) {
    let len = mountainArr.length();
    let left = 0;
    let right = len - 1;
    let top;

    while (left <= right) {
        const mid = Math.floor((left + right) / 2);
        let midH = mountainArr.get(mid);
        let midLH = mountainArr.get(mid - 1);
        let midRH = mountainArr.get(mid + 1);
        if (mid === 0 || (midLH < midH && midH < midRH)) {
            left = mid + 1;
        } else if (mid === len - 1 || (midLH > midH && midH > midRH)) {
            right = mid - 1;
        } else {
            top = mid;
            break;
        }
    }

    left = 0;
    right = top;

    while (left <= right) {
        const mid = Math.floor((left + right) / 2);
        let midH = mountainArr.get(mid);
        if (midH === target) {
            return mid;
        } else if (midH < target) {
            left = mid + 1;
        } else {
            right = mid - 1;
        }
    }

    left = top;
    right = len - 1;

    while (left <= right) {
        const mid = Math.floor((left + right) / 2);
        let midH = mountainArr.get(mid);
        if (midH === target) {
            return mid;
        } else if (midH > target) {
            left = mid + 1;
        } else {
            right = mid - 1;
        }
    }

    return -1;
};