Dsa Dp Coin Change

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

Fix coin change errors when integer overflow in large value or initialization as 0 instead of inf.

Quick Fix

Wrong

def coin(coins,amt):
    dp=[0]*(amt+1)
    for i in range(1,amt+1):
        for c in coins:
            if i>=c: dp[i]=min(dp[i],dp[i-c]+1)
    return dp[amt]

dp[0]=0, min(0, dp[i-c]+1) always returns 0. Never updates.

Right

def coin(coins,amt):
    dp=[float('inf')]*(amt+1); dp[0]=0
    for i in range(1,amt+1):
        for c in coins:
            if i>=c: dp[i]=min(dp[i],dp[i-c]+1)
    return -1 if dp[amt]==float('inf') else dp[amt]

coins=[1,2,5], amt=11 -> 3 (5+5+1). coins=[2], amt=3 -> -1.

Prevention

Initialize dp with infinity. dp[0]=0. Return -1 if dp[amt] still infinity.

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