Dont undersand why LeetCode is showing RE

#1

I ran this code over leetcode

class Solution {
int peakPresent(vector a, int n, int s, int e){
if(s < 0 || e == n){
return -1;
}
if(s <= e){
int mid = (s+e)/2;

    if( mid == 0 && a[mid+1] < a[mid]){ 
        // cout<<mid<<endl;
         return mid; }
    else if( mid == n-1 && a[mid-1] < a[mid]){
        // cout<<mid<<endl; 
         return mid;}
    else if(a[mid-1] < a[mid] && a[mid] > a[mid+1]){
        // cout<<mid<<endl; 
        return mid;}
    else if(a[mid+1] > a[mid]) {
        // cout<<mid<<"\tright"<<endl;
          return peakPresent(a,n,mid+1,e);}
    else{ 
        // cout<<mid<<"\tleft"<<endl;
     return peakPresent(a,n,s,mid);}
}
return -1;

}
public:
int findPeakElement(vector& a) {
if(a.size() == 1 )
return 0;
return peakPresent(a,a.size(),0,a.size()-1);
}

};

and it is showing
Line 924: Char 34: runtime error: addition of unsigned offset to 0x602000000370 overflowed to 0x60200000036c (stl_vector.h)
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /usr/bin/…/lib/gcc/x86_64-linux-gnu/8/…/…/…/…/include/c++/8/bits/stl_vector.h:933:34

over input: 1,2

#2

@Hyperian can you send the question link

#3
#4

@Hyperian binary search will not work for this question, you have to do a linear search and check if a[I] >a[I+1] and a[I] < a[i-1] return i

#5

it is mentioned in the question to use logn approach. Moreover, the dry run is working fine. Why its showing RE.

#6

@Hyperian you are getting re because when mid==0
array [1,2]
since a[0] is not less than a[1];
code goes to the third condition where you have wrote a[mid-1] which is -1,
so you are getting re

#7

@Hyperian third condition should be
else if(mid!=0&&mid!=a.size()-1&&a[mid-1] < a[mid] && a[mid] > a[mid+1]){
// cout<<mid<<endl;
return mid;}

#8

that worked thanks for the help

#9

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