LC.801. Minimum Swaps To Make Sequences Increasing

class Solution(object):
    def minSwap(self, A, B):
        """
         就是四个对角线元素的之间的关系
         swap[i] 表示在index = i 处发生交换使得两个数列保持递增的总swap次数
         noswap[i] 表示在index = i 处不发生交换使得两个数列保持递增的总swap次数
         注意初始值，并且每次swap后次数都要+1
        """
        swap = [float("inf")] * len(A)
        no_swap = [float("inf")] * len(A)
        for i in range(len(A)):
            if i == 0:
                swap[0], no_swap[0] = 1,0
            else:
                if A[i] > A[i-1] and B[i] > B[i-1]:
                    no_swap[i] = min(no_swap[i], no_swap[i-1])
                    swap[i] = min(swap[i], swap[i-1]+1)
                if A[i] > B[i-1] and B[i] > A[i-1]:
                    no_swap[i] = min(no_swap[i], swap[i-1])
                    swap[i] = min(swap[i], no_swap[i-1]+1)
        return min(swap[-1], no_swap[-1])