How to Fix Search in Rotated Sorted Array Errors

In this tutorial, you'll learn about How to Fix Search in Rotated Sorted Array Errors. We cover key concepts, practical examples, and best practices.

Fix search in rotated sorted array errors when pivot detection fails or binary search on rotated segment wrong.

Quick Fix

Wrong

def sr(a,t):
    l=0; r=len(a)-1
    while l<=r:
        m=l+(r-l)//2
        if a[m]==t: return m
        if a[l]<=a[m]:
            if a[l]<=t<a[m]: r=m-1
            else: l=m+1
        else:
            if a[m]<t<=a[r]: l=m+1
            else: r=m-1
    return -1

Common mistake: >= vs > in condition. If a[l]==a[m], treat as left half sorted.

Right

def sr(a,t):
    l=0; r=len(a)-1
    while l<=r:
        m=l+(r-l)//2
        if a[m]==t: return m
        if a[l]<=a[m]:
            if a[l]<=t<a[m]: r=m-1
            else: l=m+1
        else:
            if a[m]<t<=a[r]: l=m+1
            else: r=m-1
    return -1

[4,5,6,7,0,1,2], search 0 -> 4. O(log n).

Prevention

Determine which half is sorted. Check if target lies in sorted half range.

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