Dsa Greedy Gas Station

In this tutorial, you'll learn about How to Fix Gas Station Errors. We cover key concepts, practical examples, and best practices.

Fix gas station errors when total gas vs cost not checked or circuit doesn't reach start.

Quick Fix

Wrong

def can_complete(gas,cost):
    n=len(gas)
    for s in range(n):
        tank=0; possible=True
        for i in range(n):
            tank+=gas[(s+i)%n]-cost[(s+i)%n]
            if tank<0: possible=False; break
        if possible: return s
    return -1

O(n^2) simulation. Times out for large n.

Right

def can_complete(gas,cost):
    if sum(gas)<sum(cost): return -1
    tank=0; start=0
    for i in range(len(gas)):
        tank+=gas[i]-cost[i]
        if tank<0: tank=0; start=i+1
    return start

gas=[1,2,3,4,5], cost=[3,4,5,1,2] -> 3. O(n).

Prevention

If total gas < total cost: impossible. If tank falls below 0, reset start to next station.

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FAQ