2019-5-20

Author: JiayangWu

0001.两数之和/0001-两数之和.java

@@ -0,0 +1,14 @@
+class Solution {
+    public int[] twoSum(int[] nums, int target) {
+        Map<Integer, Integer> map = new HashMap<>();
+        for (int i = 0; i< nums.length; i++){
+            int complement = target - nums[i];
+            if (map.containsKey(complement)){
+                return new int[]{map.get(complement), i};
+            }
+            map.put(nums[i], i);
+        }
+        return new int[]{};
+    }
+    
+}

0004.寻找两个有序数组的中位数/0004-寻找两个有序数组的中位数.py

@@ -0,0 +1,57 @@
+from heapq import *
+class MedianFinder(object):
+# 维护两个堆，一个大顶堆，一个小顶堆，小顶堆里的数比大顶堆里的数都要大， 
+# 如果有两个潜在的中位数（两个堆size相同），数据流的中位数就是两个堆顶之和除以2
+# 如果只有一个中位数，就看size更小的那个堆的堆顶
+# 如果新进来的数比小顶堆的数要小，就把它插入大顶堆
+# 如果新进来的数比小顶堆的数要大，就把它插入小顶堆
+# 调整两个堆，使得size 差最大为1
+    def __init__(self):
+        """
+        initialize your data structure here.
+        """
+        self.max_h = list()
+        self.min_h = list()
+        heapify(self.max_h)
+        heapify(self.min_h)
+        
+
+    def addNum(self, num):
+        """
+        :type num: int
+        :rtype: None
+        """
+        heappush(self.min_h, num)
+        heappush(self.max_h, -heappop(self.min_h))
+        if len(self.max_h) > len(self.min_h):
+            heappush(self.min_h, -heappop(self.max_h))
+
+    def findMedian(self):
+        """
+        :rtype: float
+        """
+        max_len = len(self.max_h)
+        min_len = len(self.min_h)
+        if max_len == min_len: #有两个候选中位数
+            return (self.min_h[0] + -self.max_h[0]) / 2.
+        else:#小顶堆的size 一定 >= 大顶堆的size，所以答案就是小顶堆的堆顶
+            return self.min_h[0] / 1.
+            
+# Your MedianFinder object will be instantiated and called as such:
+# obj = MedianFinder()
+# obj.addNum(num)
+# param_2 = obj.findMedian()
+
+class Solution(object):
+    def findMedianSortedArrays(self, nums1, nums2):
+        """
+        :type nums1: List[int]
+        :type nums2: List[int]
+        :rtype: float
+        """
+        mf = MedianFinder()
+        for num in nums1:
+            mf.addNum(num)
+        for num in nums2:
+            mf.addNum(num)
+        return mf.findMedian()

0005.最长回文子串/0005-最长回文子串.py

@@ -0,0 +1,27 @@
+class Solution(object):
+    def longestPalindrome(self, s):
+        """
+        :type s: str
+        :rtype: str
+        """
+        max_l = 0
+        res = ""
+        for i in range(0, len(s)):
+            #以s[i] 为中心向左右扩散
+            left, right = i, i
+            while(left >= 0 and right < len(s) and s[left] == s[right]):
+                if max_l < right - left + 1:
+                    max_l = right - left + 1
+                    res = s[left:right + 1]
+                left -= 1
+                right += 1
+                        
+            #以s[i],s[i+1]为中心向左右扩散
+            left, right = i, i + 1
+            while(left >= 0 and right < len(s) and s[left] == s[right]):
+                if max_l < right - left + 1:
+                    max_l = right - left + 1
+                    res = s[left:right + 1]
+                left -= 1
+                right += 1            
+        return res

0006.Z 字形变换/0006-Z 字形变换.py

@@ -0,0 +1,35 @@
+class Solution(object):
+    def convert(self, s, n):
+        """
+        :type s: str
+        :type numRows: int
+        :rtype: str
+        """
+        #ÕÒ¹æÂÉ
+        if n <= 1:
+            return s
+        l = len(s)
+        res = ""
+        for i in range(n):
+            tmp, index = "", i
+            if i in [0, n - 1]:
+                while(index < l):
+                    
+                    tmp += s[index]
+                    index += 2 * (n - 1)
+            else:
+                state = "down"
+                while(index < l):
+                    tmp += s[index]
+                    if state == "down":
+                        state = "up"
+                        index += 2 * (n - 1 - i)
+                    else:
+                        state = "down"
+                        index += 2 * i
+            res += tmp
+
+        return res
+                    
+                        
+            

0007.整数反转/0007-整数反转.py

@@ -0,0 +1,22 @@
+class Solution(object):
+    def reverse(self, x):
+        """
+        :type x: int
+        :rtype: int
+        """
+
+        flag = 0
+        if x < 0:
+            flag = 1
+        if flag:
+            s = str(x)[1:]
+            s = s[::-1]
+            x = -1 *int(s)            
+        else:
+            s = str(x)
+            s = s[::-1]
+            x = int(s)
+            
+        if x < -1 * 2 **31 or x > 2** 31 -1:
+            return 0    
+        return x

0008.字符串转换整数 (atoi)/0008-字符串转换整数 (atoi).py

@@ -0,0 +1,36 @@
+class Solution(object):
+    def myAtoi(self, s):
+        """
+        :type str: str
+        :rtype: int
+        """
+        s = s.strip(" ")
+        if not len(s): #排除空
+            return 0
+        if s[0] not in ["+", "-"] and not s[0].isdigit(): #排除第一个非空字符不是数字
+            return 0
+        op = 1
+        res = ""
+        for i, char in enumerate(s):
+            if i == 0 :
+                if char == "-":
+                    op = -1
+                    continue
+                elif char == "+":
+                    continue
+            if char == " " or not char.isdigit():
+                break
+            res += char
+        # print res, op
+        if len(res) > 0:
+            res = op * int(res)
+        else:
+            return 0
+        INT_MIN = -2 **31
+        INT_MAX = 2 **31 - 1
+        if res > INT_MAX:
+            return INT_MAX
+        elif res < INT_MIN:
+            return INT_MIN
+        return res
+        

0011.盛最多水的容器/0011-盛最多水的容器.py

@@ -0,0 +1,20 @@
+class Solution(object):
+    def maxArea(self, height):
+        """
+        :type height: List[int]
+        :rtype: int
+        """
+        lo, hi = 0, len(height) - 1
+        res = 0
+        while(lo < hi):
+            if height[lo] > height[hi]:
+                area = height[hi] * (hi - lo)
+                hi -= 1
+            else:
+                area = height[lo] * (hi - lo)
+                lo += 1
+            # print area
+            res = max(area, res)
+            
+        return res
+                

0012.整数转罗马数字/0012-整数转罗马数字.py

@@ -0,0 +1,15 @@
+class Solution(object):
+    def intToRoman(self, num):
+        """
+        :type num: int
+        :rtype: str
+        """
+        digit = [1000,900,500,400,100,90,50,40,10,9,5,4,1]
+        mapping = {1000:"M", 900:"CM", 500:"D",400:"CD", 100:"C", 90: "XC", 50:"L",40: "XL", 10:"X", 9:"IX", 5:"V", 4:"IV", 1:"I"}
+        res = ""
+        for i in digit:
+            res += (num / i) * mapping[i]
+            num -= i * (num / i)
+            if num == 0:
+                break
+        return res

0013.罗马数字转整数/0013-罗马数字转整数.py

@@ -0,0 +1,24 @@
+class Solution(object):
+    def romanToInt(self, s):
+        """
+        :type s: str
+        :rtype: int
+        """
+        dic = {"I": 1, "V":5, "X": 10, "L":50, "C":100, "D": 500, "M": 1000}
+        stack = []
+        res = 0
+        for inx, item in enumerate(s):
+            res += dic[item]
+            # print res
+            # s.append(item)
+            if item == "V" or item == "X":
+                if stack and stack[-1] == "I":
+                    res -= 2
+            elif item == "L" or item == "C":
+                if stack and stack[-1] == "X":
+                    res -= 20
+            elif item == "D" or item == "M":
+                if stack and stack[-1] == "C":
+                    res -= 200
+            stack.append(item)
+        return res

0014.最长公共前缀/0014-最长公共前缀.py

@@ -0,0 +1,20 @@
+class Solution(object):
+    def longestCommonPrefix(self, strs):
+        """
+        :type strs: List[str]
+        :rtype: str
+        """
+        if not strs:
+            return ""
+        
+        strs.sort()
+        res = ""
+        
+        for x, y in zip(strs[0], strs[-1]):
+            if x == y:
+                res += x
+            else:
+                break
+        
+        return res
+