LeetCode 刷题记录（1-5题）

1 两数之和（题目链接）

class Solution:                # 一次哈希法
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        m = {}
        for i in range(len(nums)):
            minus = target - nums[i]
            if minus in m and i != m[minus]:
                return [i, m[minus]]
            m[nums[i]] = i
        return None

2 两数相加（题目链接）

class Solution:
    def addTwoNumbers(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        up = 0
        l3 = ListNode(0)
        l3_head = l3
        while l1 or l2:
            if l1 is None:
                l1 = ListNode(0)
            if l2 is None:
                l2 = ListNode(0)
            sum = l1.val + l2.val + up
            if sum > 9:
                sum = sum - 10
                l3.next = ListNode(sum)
                up = 1
            else:
                l3.next = ListNode(sum)
                up = 0
            l1 = l1.next
            l2 = l2.next
            l3 = l3.next
        if up > 0:
            l3.next = ListNode(up)
        return l3_head.next

3 无重复字符的最长子串（题目链接）

class Solution:
    def lengthOfLongestSubstring(self, s):
        """
        :type s: str
        :rtype: int
        """
        num = 0
        temp = []
        for item_s in s:
            if item_s in temp:
                index = temp.index(item_s) + 1
                temp = temp[index:]
                temp.append(item_s)
            else:
                temp.append(item_s)
            if len(temp) > num:
                    num = len(temp)
        return num

4 寻找两个有序数组的中位数（题目链接）

class Solution:
    def findMedianSortedArrays(self, nums1, nums2):
        """
        :type nums1: List[int]
        :type nums2: List[int]
        :rtype: float
        """
        sum = (len(nums1) + len(nums2))
        index = sum//2 + 1
        p1 = 0
        p2 = 0
        max1 = 0
        max2 = 0           

        for item in range(index):
            max2 = max1

            if p1 == len(nums1):
                max1 = nums2[p2]
                p2 += 1
            elif p2 == len(nums2):
                max1 = nums1[p1]
                p1 += 1
            elif nums1[p1] > nums2[p2]:
                max1 = nums2[p2]
                p2 += 1
            else:
                max1 = nums1[p1]
                p1 += 1

        if sum%2 == 1:
            return max1
        else:
            return (max1 + max2)/2

5 最长回文子串（题目链接）

Manacher算法（“马拉车算法”，中心扩展法+不重复判断）

讲解链接：https://www.jianshu.com/p/116aa58b7d81

https://www.cnblogs.com/nkqlhqc/p/9005450.html

class Solution:
    def longestPalindrome(self, s):
        """
        :type s: str
        :rtype: str
        """
        if s == '':
            return ''

        sp = ''
        sp_len = 2*len(s)+2
        radius = [0 for o in range(sp_len)]            # 回文半径列表
        index_max = -1                                 # 最大回文子串中间所在index
        r_max = -1                                     # 最大回文子串右边界

        def plalindrome(index, r_i=1):
            while(sp[index-r_i] != '$' and sp[index+r_i] != '$' and sp[index-r_i] == sp[index+r_i]):
                r_i += 1
            return r_i

        for item in range(len(s)):                      # 字符串的字符间加'#'与'$'
            sp += ''.join(['#', s[item]])
        sp = ''.join(['$', sp, '#$'])

        for i in range(sp_len):                         # 计算回文半径，填充半径列表
            if i >= r_max:
                radius[i] = plalindrome(i)
                if r_max < radius[i]:
                    r_max = radius[i]
                    index_max = i
            elif r_max - i <= radius[2 * index_max - i]:
                radius[i] = radius[2 * index_max - i]
            else:
                radius[i] = plalindrome(i, radius[2 * index_max - i] + 1)
                if r_max < radius[i]:
                    r_max = radius[i]
                    index_max = i
        result = sp[index_max - radius[index_max] + 1: index_max + radius[index_max]]
        return result.replace('#', '')