数组中的逆序对.py

'''
在数组中的两个数字，如果前面一个数字大于后面的数字，则这两个数字组成一个逆序对。
输入一个数组,求出这个数组中的逆序对的总数P。
'''

# -*- coding:utf-8 -*-
class Solution:
    def InversePairs(self, data):
        length = len(data)
        if data == None or length <= 0:
            return 0
        copy = [0]*length
        for i in range(length):
            copy[i] = data[i]

        count = self.InversePairsCore(data, copy, 0, length-1)
        return count
    def InversePairsCore(self, data, copy, start, end):
        if start == end:
            copy[start] = data[start]
            return 0
        length = (end - start)//2
        left = self.InversePairsCore(copy, data, start, start+length)
        right = self.InversePairsCore(copy, data, start+length+1, end)

        # i初始化为前半段最后一个数字的下标
        i = start + length
        # j初始化为后半段最后一个数字的下标
        j = end

        indexCopy = end
        count = 0
        while i >= start and j >= start+length+1:
            if data[i] > data[j]:
                copy[indexCopy] = data[i]
                indexCopy -= 1
                i -= 1
                count += j - start - length
            else:
                copy[indexCopy] = data[j]
                indexCopy -= 1
                j -= 1

        while i >= start:
            copy[indexCopy] = data[i]
            indexCopy -= 1
            i -= 1
        while j >= start+length+1:
            copy[indexCopy] = data[j]
            indexCopy -= 1
            j -= 1
        return left + right + count

    # 使用数据的index进行求解
    def InversePairs2(self, data):
        if len(data) <= 0:
            return 0
        count = 0
        copy = []
        for i in range(len(data)):
            copy.append(data[i])
        copy.sort()
        i = 0
        while len(copy) > i:
            count += data.index(copy[i])
            data.remove(copy[i])
            i += 1
        return count

s = Solution()
print(s.InversePairs2([364,637,341,406,747,995,234,971,571,219,993,407,416,366,315,301,601,650,418,355,460,505,360,965,516,648,727,667,465,849,455,181,486,149,588,233,144,174,557,67,746,550,474,162,268,142,463,221,882,576,604,739,288,569,256,936,275,401,497,82,935,983,583,523,697,478,147,795,380,973,958,115,773,870,259,655,446,863,735,784,3,671,433,630,425,930,64,266,235,187,284,665,874,80,45,848,38,811,267,575]))