homework-4

Author: zhangbingxu

4th/homework_1/id_100/64.MinimumPathSum_100.py

@@ -0,0 +1,21 @@
+class Solution(object):
+    def minPathSum(self, grid):
+        """
+        :type grid: List[List[int]]
+        :rtype: int
+        """
+        m = len(grid)
+        n = len(grid[0])
+
+        for i in range(m):
+            for j in range(n):
+                if i == 0 and j == 0:
+                    grid[i][j] = grid[i][j]
+                elif i == 0:
+                    grid[i][j] = grid[i][j] + grid[i][j - 1]
+                elif j == 0:
+                    grid[i][j] = grid[i][j] + grid[i - 1][j]
+                else:
+                    grid[i][j] = grid[i][j] + min(grid[i - 1][j], grid[i][j - 1])
+        
+        return grid[m - 1][n - 1]

4th/homework_2/id_100/121.BestTimetoBuyandSellStock_100.py

@@ -0,0 +1,18 @@
+class Solution(object):
+    def maxProfit(self, prices):
+        """
+        :type prices: List[int]
+        :rtype: int
+        """
+        if not prices: return 0
+        profit = 0
+        min = prices[0]
+        l = len(prices)
+        for i in range(l):
+            if prices[i] < min:
+                min = prices[i]
+            else:
+                if profit < prices[i] - min:
+                    profit = prices[i] - min;
+
+        return profit

4th/homework_3/id_100/122.BestTimetoBuyandSellStockII_100.py

@@ -0,0 +1,15 @@
+class Solution(object):
+    def maxProfit(self, prices):
+        """
+        :type prices: List[int]
+        :rtype: int
+        """
+        if not prices: return 0
+        profit = 0
+        i = 1
+        while i < len(prices):
+            if prices[i] - prices[i - 1] > 0:
+                profit += prices[i] - prices[i - 1]
+            i = i + 1
+
+        return profit

4th/homework_4/id_100/70.ClimbingStairs_100.py

@@ -0,0 +1,17 @@
+class Solution(object):
+    def climbStairs(self, n):
+        """
+        :type n: int
+        :rtype: int
+        """
+        if n == 0: return 0
+        if n == 1: return 1
+        if n == 2: return 2
+        
+        res = [0 for i in range(n)]
+        res[0], res[1] = 1, 2
+
+        for i in range(2, n):
+            res[i] = res[i - 1] + res[i - 2]
+        
+        return res[n - 1]

4th/homework_5/id_100/198.HouseRobber_100.py

@@ -0,0 +1,17 @@
+class Solution(object):
+    def rob(self, nums):
+        """
+        :type nums: List[int]
+        :rtype: int
+        """
+        n = len(nums)
+        if n == 0: return 0
+        if n == 1: return nums[0]
+        if n == 2: return max(nums[0], nums[1])
+        
+        nums[0] = nums[0]
+        nums[1] = max(nums[0], nums[1])
+        for i in range(2, n):
+            nums[i] = max(nums[i] + nums[i - 2], nums[i - 1])
+        
+        return nums[n - 1]

4th/homework_6/id_100/120.Triangle_100.py

@@ -0,0 +1,18 @@
+class Solution(object):
+    def minimumTotal(self, triangle):
+        """
+        :type triangle: List[List[int]]
+        :rtype: int
+        """
+        
+        if not triangle: return 0
+
+        n = len(triangle)
+        for i in range(n, 0, -1):
+            for j in range(len(triangle[i - 1])):
+                if i == n:
+                    triangle[i - 1][j] = triangle[i - 1][j]
+                else:
+                    triangle[i - 1][j] = triangle[i - 1][j] + min(triangle[i][j], triangle[i][j + 1])
+
+        return triangle[0][0]

4th/homework_7/id_100/152.MaximumProductSubarray_100.py

@@ -0,0 +1,18 @@
+class Solution(object):
+    def maxProduct(self, nums):
+        """
+        :type nums: List[int]
+        :rtype: int
+        """
+        if not nums: return 0
+
+        result = nums[0]
+        minNum, maxNum = result, result
+        for i in range(1, len(nums)):
+            temp = maxNum
+            maxNum = max(max(nums[i] * temp, nums[i] * minNum), nums[i])
+            minNum = min(min(nums[i] * temp, nums[i] * minNum), nums[i])
+            result = max(maxNum, result)
+            
+        return result
+    

4th/homework_8/id_100/213.HouseRobberII_100.py

@@ -0,0 +1,27 @@
+class Solution(object):
+    def rob(self, nums):
+        """
+        :type nums: List[int]
+        :rtype: int
+        """
+        n = len(nums)
+        if n == 0: return 0
+        if n == 1: return nums[0]
+        if n == 2: return max(nums[0], nums[1])
+        
+        pre1 = 0
+        result1 = 0
+        for i in range(1, n):
+            temp = pre1
+            pre1 = result1
+            result1 = max(temp + nums[i], pre1)
+
+        pre2 = 0
+        result2 = 0
+        for i in range(0, n - 1):
+            temp = pre2
+            pre2 = result2
+            result2 = max(temp + nums[i], pre2)
+
+        return max(result1, result2)
+    

4th/homework_9/id_100/322.CoinChange_100.py

@@ -0,0 +1,28 @@
+# UNDONE
+# Status: Time Limit Exceeded
+
+
+class Solution(object):
+    def coinChange(self, coins, amount):
+        """
+        :type coins: List[int]
+        :type amount: int
+        :rtype: int
+        """
+
+        if not amount:
+            return 0
+
+        count = amount + 1
+        for i in range(len(coins)):
+            curr_val = 0
+            if amount >= coins[i]:
+                next_val = self.coinChange(coins, amount - coins[i])
+                if next_val > -1:
+                    curr_val = 1 + next_val
+            if curr_val > 0:
+                count = min(count, curr_val)
+
+        if count == amount + 1:
+            count = -1
+        return count