Question

def fastMaxVal(w, v, i, aW):
    global numCalls
    numCalls += 1
    try: return m[(i, aW)]
    except KeyError:
        if i == 0:
            if w[i] <= aW:
                m[(i, aW)] = v[i]
                return v[i]
            else:
                m[(i, aW)] = 0
                return 0
        without_i = fastMaxVal(w, v, i-1, aW)
        if w[i] > aW:
            m[(i, aW)] = without_i
            return without_i
        else:
            with_i = v[i] + fastMaxVal(w, v, i-1, aW - w[i])
        res = max(with_i, without_i)
        m[(i, aW)] = res
        return res

def maxVal0(w, v, i, aW):
    m = {}
    return fastMaxVal

weights = [1, 1, 5, 5, 3, 3, 4, 4]
vals = [15, 15, 10, 10, 9, 9, 5, 5]
numCalls = 0
res = maxVal0(weights, vals, len(vals) - 1, 8)
print ('max Val =', res, 'number of calls =', numCalls)

该程序约为01Knapsack问题。我使用决策树来解决问题。但是，我运行该程序并得到以下结果。

max Val =函数fastMaxVal位于0x03BB7390次数= 0

我的计划出了什么问题？

Answer 1

在maxVal0函数中，您将返回fastMaxVal函数本身，而不是其调用结果。

我认为应该是这样的：

def maxVal0(w, v, i, aW):
    m = {}
    return fastMaxVal(w, v, i, aW)

此外，您的fastMaxVal正在使用m，但它不在其范围内。

Answer 2

def fastMaxVal(w, v, i, aW, m):
    global numCalls
    numCalls += 1
    try: return m[(i, aW)]
    except KeyError:
        if i == 0:
            if w[i] <= aW:
                m[(i, aW)] = v[i]
                return v[i]
            else:
                m[(i, aW)] = 0
                return 0
        without_i = fastMaxVal(w, v, i-1, aW, m)
        if w[i] > aW:
            m[(i, aW)] = without_i
            return without_i
        else:
            with_i = v[i] + fastMaxVal(w, v, i-1, aW - w[i], m)
        res = max(with_i, without_i)
        m[(i, aW)] = res
        return res

def maxVal0(w, v, i, aW):
    m = {}
    return fastMaxVal(w, v, i, aW, m)

weights = [1, 1, 5, 5, 3, 3, 4, 4]
vals = [15, 15, 10, 10, 9, 9, 5, 5]
numCalls = 0
res = maxVal0(weights, vals, len(vals) - 1, 8)
print ('max Val =', res, 'number of calls =', numCalls)

我把右边放在上面。我将结果附在如下。

最大值= 48次呼叫= 50

输出错误为0x03BB7390

2 个答案: