第四章 分治策略

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暴力求解法

我们可以穷举所有的买入卖出组合，效率是n的平方

问题转换

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使用分治法求解

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我们来看下跨域中电的情况

FindMaxCrossMid(A,l,m,r)
leftSum = -无穷大
sum = 0
for i = m downto l
      sum = sum+ A[i]
      if sum > leftSum
        leftSum = sum
        minL = i

rightSum = -无穷大
sum = 0
for i = m+1upto r
      sum = sum+ A[i]
      if sum > rightSum
        rightSum = sum
        maxR = i
return(minL,maxR,leftSum+rightSum)

FindMaxNum(A,low,high)
if hight == low return(low,high, A[low])
mid = [low+high]/2
(l-low,l-high,l-value) = FindMaxNum(A,low,mid)
(r-low,r-high,r-value) = FindMaxNum(A,mid+1,high)
(c-low,c-high,c-value) = FindMaxCrossMid(A,low,mid,high)
if l-value> c-value and l-value>r-value return (l-low,l-high,l-value)
if r-value> l-value and r-value > c-value return  (r-low,r-high,r-value)
return (c-low,c-high,c-value)

矩阵乘法的Strassen乘法