add more solutions

Binary Tree Maximum Path Sum.py

@@ -0,0 +1,13 @@
+class Solution:
+    maxSum = -2147483648
+    def maxPathSum(self, root):
+        self.maxPathRecur(root)
+        return self.maxSum
+
+    def maxPathRecur(self, root):
+        if root == None:
+            return 0
+        left = max(0, self.maxPathRecur(root.left))
+        right = max(0, self.maxPathRecur(root.right))
+        self.maxSum = max(self.maxSum, left + right + root.val)
+        return root.val + max(left, right)

Clone Graph.py

@@ -0,0 +1,19 @@
+class Solution:
+    def cloneGraph(self, node):
+        if node == None:
+            return None
+        start = UndirectedGraphNode(node.label)
+        map, current = {node: start}, [node]
+        while len(current) > 0:
+            next = []
+            for x in current:
+                for neighbor in x.neighbors:
+                    if neighbor not in map:
+                        neighbor_copy = UndirectedGraphNode(neighbor.label)
+                        next.append(neighbor)
+                        map[x].neighbors.append(neighbor_copy)
+                        map[neighbor] = neighbor_copy
+                    else:
+                        map[x].neighbors.append(map[neighbor])
+            current = next
+        return start

Decode Ways.py

@@ -0,0 +1,13 @@
+class Solution:
+    def numDecodings(self, s):
+        if len(s) == 0:
+            return 0
+        prev, prev_prev = 1, 0
+        for i in range(len(s)):
+            current = 0
+            if s[i] != '0':
+                current = prev
+            if i > 0 and (s[i - 1] == "1" or (s[i - 1] == "2" and s[i] <= "6")):
+                current += prev_prev
+            prev, prev_prev = current, prev
+        return prev

Distinct Subsequences.py

@@ -0,0 +1,11 @@
+class Solution:
+    def numDistinct(self, S, T):
+        ways = [[0 for j in range(len(S) + 1)] for i in range(len(T) + 1)]
+        for i in range(len(S) + 1):
+            ways[0][i] = 1
+        for i in range(1, len(T) + 1):
+            for j in range(1, len(S) + 1):
+                ways[i][j] = ways[i][j - 1]
+                if T[i - 1] == S[j - 1]:
+                    ways[i][j] += ways[i - 1][j - 1]
+        return ways[len(T)][len(S)]

Gas Station.py

@@ -0,0 +1,14 @@
+class Solution:
+    def canCompleteCircuit(self, gas, cost):
+        start, sum_so_far, sum = 0, 0, 0
+        for i in range(len(gas)):
+            diff = gas[i] - cost[i]
+            if sum_so_far + diff < 0:
+                start = i + 1
+                sum_so_far = 0
+            else:
+                sum_so_far += diff
+            sum += diff
+        if sum >= 0:
+            return start
+        return -1

Implement strStr().py

@@ -0,0 +1,11 @@
+class Solution:
+    def strStr(self, haystack, needle):
+        for i in range(len(haystack) - len(needle) + 1):
+            found = True
+            for j in range(len(needle)):
+                if haystack[i + j] != needle[j]:
+                    found = False
+                    break
+            if found:
+                return haystack[i:]
+        return None

Insert Interval.py

@@ -0,0 +1,16 @@
+class Solution:
+    def insert(self, intervals, newInterval):
+        return self.merge(intervals + [newInterval])
+
+    def merge(self, intervals):
+        if len(intervals) == 0:
+            return intervals
+        intervals.sort(key = lambda x: x.start)
+        result = [intervals[0]]
+        for i in range(1, len(intervals)):
+            current, prev = intervals[i], result[-1]
+            if current.start <= prev.end:
+                prev.end = max(prev.end, current.end)
+            else:
+                result.append(current)
+        return result

Largest Rectangle in Histogram.py

@@ -0,0 +1,14 @@
+class Solution:
+    def largestRectangleArea(self, height):
+        increasing, area, i = [], 0, 0
+        while i <= len(height):
+            if len(increasing) == 0 or (i < len(height) and height[i] > height[increasing[-1]]):
+                increasing.append(i)
+                i += 1
+            else:
+                last = increasing.pop()
+                if len(increasing) == 0:
+                    area = max(area, height[last] * i)
+                else:
+                    area = max(area, height[last] * (i - increasing[-1] - 1))
+        return area

Longest Substring Without Repeating Characters.py

@@ -0,0 +1,14 @@
+class Solution:
+    def lengthOfLongestSubstring(self, s):
+        count, start, longest = [False for i in range(256)], 0, 0
+        for i in range(len(s)):
+            if count[ord(s[i])] == False:
+                count[ord(s[i])] = True
+            else:
+                longest = max(i - start, longest)
+                while s[start] != s[i]:
+                    count[ord(s[start])] = False
+                    start += 1
+                start += 1
+        longest = max(len(s) - start, longest)
+        return longest

Longest Valid Parentheses.py

@@ -0,0 +1,15 @@
+class Solution:
+    def longestValidParentheses(self, s):
+        longest, last, indices = 0, 0, []
+        for i in range(len(s)):
+            if s[i] == '(':
+                indices.append(i)
+            elif len(indices) == 0:
+                last = i + 1
+            else:
+                index = indices.pop()
+                if len(indices) == 0:
+                    longest = max(longest, i - last + 1)
+                else:
+                    longest = max(longest, i - indices[-1])
+        return longest

Maximal Rectangle.py

@@ -0,0 +1,27 @@
+class Solution:
+    def maximalRectangle(self, matrix):
+        heights = [[0 for j in range(len(matrix[0]))] for i in range(len(matrix))]
+        for i in range(0, len(matrix)):
+            for j in range(len(matrix[0])):
+                if matrix[i][j] == "0":
+                    heights[i][j] = 0
+                elif i == 0:
+                    heights[i][j] = 1
+                else:
+                    heights[i][j] = int(heights[i - 1][j]) + 1
+        return reduce(lambda acc, i: max(acc, self.largestRectangleArea(heights[i])), range(len(heights)), 0)
+
+    # This is the solution for question Largest Rectangle in Histogram
+    def largestRectangleArea(self, height):
+        increasing, area, i = [], 0, 0
+        while i <= len(height):
+            if len(increasing) == 0 or (i < len(height) and height[i] > height[increasing[-1]]):
+                increasing.append(i)
+                i += 1
+            else:
+                last = increasing.pop()
+                if len(increasing) == 0:
+                    area = max(area, height[last] * i)
+                else:
+                    area = max(area, height[last] * (i - increasing[-1] - 1))
+        return area

Merge Intervals.py

@@ -0,0 +1,13 @@
+class Solution:
+    def merge(self, intervals):
+        if len(intervals) == 0:
+            return intervals
+        intervals.sort(key = lambda x: x.start)
+        result = [intervals[0]]
+        for i in range(1, len(intervals)):
+            current, prev = intervals[i], result[-1]
+            if current.start <= prev.end:
+                prev.end = max(prev.end, current.end)
+            else:
+                result.append(current)
+        return result

Permutation Sequence.py

@@ -0,0 +1,12 @@
+class Solution:
+    def getPermutation(self, n, k):
+        seq, k, fact = "", k - 1, math.factorial(n - 1)
+        perm = [i for i in range(1, n + 1)]
+        for i in reversed(range(n)):
+            curr = perm[k / fact]
+            seq += str(curr)
+            perm.remove(curr)
+            if i > 0:
+                k %= fact
+                fact /= i
+        return seq

Restore IP Addresses.py

@@ -0,0 +1,22 @@
+class Solution:
+    def restoreIpAddresses(self, s):
+        result = []
+        self.restoreIpAddressesRecur(result, s, "", 0)
+        return result
+
+    def restoreIpAddressesRecur(self, result, s, current, dots):
+        # pruning to improve performance
+        if (4 - dots) * 3 < len(s):
+            return
+        if dots == 3:
+            if self.isValid(s):
+                result.append(current + s)
+        else:
+            for i in range(3):
+                if len(s) > i and self.isValid(s[:i + 1]):
+                    self.restoreIpAddressesRecur(result, s[i + 1:], current + s[:i + 1] + '.', dots + 1)
+
+    def isValid(self, s):
+        if len(s) == 0 or (s[0] == "0" and s != "0"):
+            return False
+        return int(s) < 256

Simplify Path.py

@@ -0,0 +1,10 @@
+class Solution:
+    def simplifyPath(self, path):
+        stack, tokens = [], path.split('/')
+        for token in tokens:
+            if token == "..":
+                if len(stack) > 0:
+                    stack.pop()
+            elif token != "" and token != ".":
+                stack.append(token)
+        return "/" + reduce(lambda acc, x: acc + x + "/", stack, "")[:-1]

Sqrt(x).py

@@ -0,0 +1,10 @@
+class Solution:
+    def sqrt(self, x):
+        low, high = 0, x / 2 + 1
+        while high >= low:
+            mid = (high + low) / 2
+            if x < mid * mid:
+                high = mid - 1
+            else:
+                low = mid + 1
+        return int(high)

Word Search.py

@@ -0,0 +1,18 @@
+class Solution:
+    def exist(self, board, word):
+        visited = [[0 for y in range(len(board[0]))] for x in range(len(board))]
+        for i in range(len(board)):
+            for j in range(len(board[0])):
+                if self.existRecur(board, word, visited, i, j) == True:
+                    return True
+        return False
+
+    def existRecur(self, board, word, visited, i, j):
+        if len(word) == 0:
+            return True
+        if i >= len(board) or j >= len(board[0]) or i < 0 or j < 0 or visited[i][j] == 1 or board[i][j] != word[0]:
+            return False
+        visited[i][j] = 1
+        found = self.existRecur(board, word[1:], visited, i + 1, j) or self.existRecur(board, word[1:], visited, i - 1, j) or self.existRecur(board, word[1:], visited, i, j + 1) or self.existRecur(board, word[1:], visited, i, j - 1)
+        visited[i][j] = 0
+        return found

ZigZag Conversion.py

@@ -0,0 +1,13 @@
+class Solution:
+    def convert(self, s, nRows):
+        step, zigzag = 2 * nRows - 2, ""
+        if s == None or len(s) == 0 or nRows <= 0:
+            return ""
+        if nRows == 1:
+            return s
+        for i in range(nRows):
+            for j in range(i, len(s), step):
+                zigzag += s[j]
+                if i > 0 and i < nRows - 1 and j + step - 2 * i < len(s):
+                    zigzag += s[j + step - 2 * i]
+        return zigzag