找零錢的算法

1. 很慢的遞歸解決方案

# 遞歸版本
def recMC(coinValueList, change):
    minCoins = change
    if change in coinValueList:
        return 1
    else:
        for i in [c for c in coinValueList if c < change]:
            numCoins = 1 + recMC(coinValueList, change-i)
            if numCoins < minCoins:
                minCoins = numCoins
    return minCoins


print(recMC([1,5,10,25], 63))

2. 添加了查詢表的找零算法

def recDC(coinValueList, change, knownResults):
    start = time.time()
    minCoins = change
    if change in coinValueList:
        knownResults[change] = 1
        return 1
    elif knownResults[change] > 0:
        return knownResults[change]
    else:
        for i in [c for c in coinValueList if c < change]:
            numCoins = 1 + recDC(coinValueList, change-i, knownResults)
            if numCoins < minCoins:
                minCoins = numCoins
                knownResults[change] = minCoins
    end = time.time()
    length = end - start
    print(length)

    return minCoins

3.動態規劃版本的找零算法

# 動態規劃版本找零問題
def dpMakeChange(coinValueList, change, minCoins, coinUsed):
    for cents in range(change+1):
        coinCount = cents
        new_coin = 1
        for j in [c for c in coinValueList if c <= cents]:
            if minCoins[cents-j] + 1 < coinCount:
                coinCount = minCoins[cents-j] + 1
                new_coin = j
        minCoins[cents] = coinCount
        coinUsed[cents] = new_coin
    return minCoins[change]


def printCoins(coinsUsed, change):
    coin = change
    while coin > 0:
        thisCoin = coinsUsed[coin]
        print(thisCoin)
        coin = coin - thisCoin

c1 = [1,5,10,21,25]
coinUsed = [0]*64
coinCount = [0]*64

cnt = dpMakeChange(c1, 63, coinCount, coinUsed)
print(cnt)

printCoins(coinUsed, 63)
printCoins(coinUsed, 52)

output:
3
21
21
21
10
21
21