Find Peak Element

Find Peak Element

A peak element is an element, which is greater than its neighbors.

Given an input array where num[i] ≠ num[i+1] , the find a peak element and return its index.

The array may be contain multiple peaks, in this case return the index to any one of the peaks is fine.

May imagine num[-1] = num[n] = -∞ .

For example, in array [1, 2, 3, 1] , 3 is a peak element and your function should return the index number 2.

I write my own a bit less, this problem to be used to find two points to achieve. But I never understood why it was possible to use binary search to achieve

1  Public classSolution {2      Public intFindpeakelement (int[] num) {3         if(Num.length = = 0 | | num.length = = 1)4             return0;5         BooleanISINCR =false;//is ascending6         intindex =-1;//Peak Index value7         intNumarray[] =New int[Num.length + 2];8          for(inti = 0; I < num.length;i++){9Numarray[i + 1] =Num[i];Ten         } OneNumarray[0] =Integer.min_value; ANUMARRAY[NUMARRAY.LENGTH-1] =Integer.min_value; -          -          for(inti = 1; I < numarray.length;i++){ the             if(Numarray[i] > Numarray[i-1]) -ISINCR =true; -             if(ISINCR && Numarray[i] < numarray[i-1]){ -index = i-2; +                  Break; -             } +         } A          at         returnindex; -     } -}

The following is Baidu to, as if it is csdn or where, I am too lazy to find the source of origin. This time complexity is O (N)

1  Public classSolution {2      Public intFindpeakelement (int[] num) {3          for(inti = 1; i < num.length; i++){4             if(Num[i] < num[i-1])5                 returnI-1;6         }7         returnNum.length-1;8     }9}

Here is the discussion area with a binary search implementation

1  Public classSolution {2      Public intFindpeakelement (int[] num) {3         intLow = 0;4         intHigh = Num.length-1;5          while(Low <High ) {6             intMid = (low + high + 1)/2;7             if(Mid = = 0 | | num[mid] > NUM[MID-1]) {8Low =mid;9}Else {TenHigh = Mid-1; One             } A         } -         returnLow ; -     } the}

Find Peak Element