leetcode162寻找峰值

题目：

162. Find Peak Element
     Medium
     9.1K
     4.3K
     Companies
     A peak element is an element that is strictly greater than its neighbors.

Given a 0-indexed integer array nums, find a peak element, and return its index. If the array contains multiple peaks, return the index to any of the peaks.

You may imagine that nums[-1] = nums[n] = -∞. In other words, an element is always considered to be strictly greater than a neighbor that is outside the array.
//！！ 这里的意思是说！！如果边界值0 or 最后一个or或者就它一个（即长度为1），并且周边的那一个满足条件，也满足条件，所以要做临界值判断
You must write an algorithm that runs in O(log n) time.

var findPeakElement = function(nums) {
 let left=0;
 let right=nums.length-1;

 if(nums.length==1){
     return 0;  //！！临界值判断，只有它自己
 }
 while(left<=right){
     let mid=Math.floor(left+(right-left)/2);

     if(mid==nums.length-1 && nums[mid]>nums[mid-1] || mid==0 && nums[mid]>nums[mid+1]){
         return mid;
     }         //！！这里是临界值判断 只有一个临界值
      if(nums[mid]<nums[mid+1]){
         left=mid+1;
     }
     else if(nums[mid]<nums[mid-1]){
         right=mid-1;
     }
     else{
         return mid;
     }
 }

return -1;
};

最后一个条件写清除一点也行

var findPeakElement = function(nums) {
 let left=0;
 let right=nums.length-1;

 if(nums.length==1){
     return 0;
 }
 while(left<=right){
     let mid=Math.floor(left+(right-left)/2);

     if(mid==nums.length-1 && nums[mid]>nums[mid-1] || mid==0 && nums[mid]>nums[mid+1]){
         return mid;
     }
      if(nums[mid]<nums[mid+1]){
         left=mid+1;
     }
     else if(nums[mid]<nums[mid-1]){
         right=mid-1;
     }
     else if(nums[mid]>nums[mid+1] && nums[mid]>nums[mid-1]){
         return mid;
     }
 }

return -1;
};