112 lines
2.7 KiB
JavaScript
112 lines
2.7 KiB
JavaScript
/**
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* LeetCode 852. 山脉数组的峰顶索引
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* @param {number[]} A
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* @return {number}
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*/
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export const peakIndexInMountainArray = function (A) {
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let left = 0
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let right = A.length - 1
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while (left < right) {
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const mid = left + ((right - left) >> 1)
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if (A[mid] > A[mid - 1] && A[mid] > A[mid + 1]) return mid
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if (A[mid] < A[mid + 1] && A[mid] > A[mid - 1]) {
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left = mid
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} else {
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right = mid
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}
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}
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return 0
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}
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/**
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* LintCode 585. 山脉序列中的最大值
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* @param nums: a mountain sequence which increase firstly and then decrease
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* @return: then mountain top
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*/
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export const mountainSequence = function (nums) {
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let left = 0
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let right = nums.length - 1
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while (left < right) {
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const mid = left + ((right - left) >> 1)
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if (nums[mid] > nums[mid - 1] && nums[mid] > nums[mid + 1]) return nums[mid]
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if (nums[mid] < nums[mid + 1] && nums[mid] > nums[mid - 1]) {
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left = mid
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} else {
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right = mid
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}
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}
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return nums[0]
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}
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/**
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* // This is the MountainArray's API interface.
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* // You should not implement it, or speculate about its implementation
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* function MountainArray() {
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* @param {number} index
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* @return {number}
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* this.get = function(index) {
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* ...
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* };
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*
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* @return {number}
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* this.length = function() {
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* ...
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* };
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* };
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*/
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/**
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* 1095. 山脉数组中查找目标值
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* @param {number} target
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* @param {MountainArray} mountainArr
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* @return {number}
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*/
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export const findInMountainArray = function (target, mountainArr) {
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let left = 0
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let right = mountainArr.length() - 1
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// 山峰索引
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let peak = 0
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while (left < right) {
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const mid = left + ((right - left) >> 1)
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if (mountainArr.get(mid) > mountainArr.get(mid - 1) && mountainArr.get(mid) > mountainArr.get(mid + 1)) {
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peak = mid
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break
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}
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if (mountainArr.get(mid) < mountainArr.get(mid + 1) && mountainArr.get(mid) > mountainArr.get(mid - 1)) {
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left = mid
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} else {
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right = mid
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}
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}
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// 在山峰左边查找
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const index = binarySearch(mountainArr, target, 0, peak, v => v)
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// 若存在，则直接返回下标，否则在山峰右边查找
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return index !== -1 ? index : binarySearch(mountainArr, target, peak + 1, mountainArr.length() - 1, v => -v)
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// 二分法查找
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// 其中 fn 是用来对升序还是降序的特殊处理
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function binarySearch (mountainArr, target, l, r, fn) {
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target = fn(target)
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while (l <= r) {
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const mid = (l + (r - l) / 2) | 0
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const cur = fn(mountainArr.get(mid))
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if (cur === target) {
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return mid
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} else if (cur < target) {
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l = mid + 1
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} else {
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r = mid - 1
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}
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}
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return -1
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}
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}
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