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Merge pull request #14 from mihirs16/master

added leetcode questions

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	`1`	`+# find if path exists in a graph \| leetcode 1971 \| https://leetcode.com/problems/find-if-path-exists-in-graph/`
	`2`	`+# method: adjacency list, visited and toVisit lists`
	`3`	`+`
	`4`	`+from collections import defaultdict`
	`5`	`+`
	`6`	`+class Solution:`
	`7`	`+ def validPath(self, n: int, edges: list[list[int]], source: int, destination: int) -> bool:`
	`8`	`+ # edge case`
	`9`	`+ if n == 1 and source == destination:`
	`10`	`+ return True`
	`11`	`+`
	`12`	`+ edgeMap = defaultdict(list) # adjacency list`
	`13`	`+ for edge in edges:`
	`14`	`+ edgeMap[edge[0]].append(edge[1])`
	`15`	`+ edgeMap[edge[1]].append(edge[0])`
	`16`	`+`
	`17`	`+ visited = set() # set of visited nodes`
	`18`	`+ toVisit = [edgeMap[source]] # set of nodes to visit`
	`19`	`+`
	`20`	`+ # while there are nodes to visit`
	`21`	`+ while toVisit:`
	`22`	`+`
	`23`	`+ # this node is now visited`
	`24`	`+ nodes = toVisit.pop()`
	`25`	`+`
	`26`	`+ # for each node in the adjacent nodes`
	`27`	`+ for node in nodes:`
	`28`	`+ if node == destination:`
	`29`	`+ return True`
	`30`	`+`
	`31`	`+ # if node wasn't visited`
	`32`	`+ # visit its adjacent nodes`
	`33`	`+ elif node not in visited:`
	`34`	`+ visited.add(node)`
	`35`	`+ toVisit.append(edgeMap[node])`
	`36`	`+`
	`37`	`+ # if node was visited`
	`38`	`+ # do nothing`
	`39`	`+`
	`40`	`+ # if no more nodes to visit`
	`41`	`+ # and still no path`
	`42`	`+ return False`

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	`1`	`+# count nodes equal to average of subtree \| leetcode 2265 \| https://leetcode.com/problems/count-nodes-equal-to-average-of-subtree/`
	`2`	`+# method: dfs, update size and sum of subtree at each node and check for average`
	`3`	`+`
	`4`	`+# Definition for a binary tree node.`
	`5`	`+class TreeNode:`
	`6`	`+ def __init__(self, val=0, left=None, right=None):`
	`7`	`+ self.val = val`
	`8`	`+ self.left = left`
	`9`	`+ self.right = right`
	`10`	`+`
	`11`	`+class Solution:`
	`12`	`+ def averageOfSubtree(self, root: list[TreeNode]) -> int:`
	`13`	`+ self.counter = 0`
	`14`	`+ def dfs(node):`
	`15`	`+ if node is None:`
	`16`	`+ return 0, 0`
	`17`	`+`
	`18`	`+ lSize, lSum = dfs(node.left)`
	`19`	`+ rSize, rSum = dfs(node.right)`
	`20`	`+`
	`21`	`+ nSize, nSum = lSize + rSize + 1, lSum + rSum + node.val`
	`22`	`+ if (nSum // nSize) == node.val:`
	`23`	`+ self.counter += 1`
	`24`	`+`
	`25`	`+ return nSize, nSum`
	`26`	`+`
	`27`	`+ dfs(root)`
	`28`	`+ return self.counter`
	`29`	`+`

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	`1`	`+# evaluate boolean binary tree \| leetcode 2331 \| https://leetcode.com/problems/evaluate-boolean-binary-tree/`
	`2`	`+# method: dfs, evaluate left and/or right, return node's value`
	`3`	`+`
	`4`	`+# Definition for a binary tree node.`
	`5`	`+class TreeNode:`
	`6`	`+ def __init__(self, val=0, left=None, right=None):`
	`7`	`+ self.val = val`
	`8`	`+ self.left = left`
	`9`	`+ self.right = right`
	`10`	`+`
	`11`	`+class Solution:`
	`12`	`+ def evaluateTree(self, node):`
	`13`	`+ if node.left is None and node.right is None:`
	`14`	`+ return node.val`
	`15`	`+`
	`16`	`+ if node.val == 2:`
	`17`	`+ node.val = bool(self.evaluateTree(node.left)) or bool(self.evaluateTree(node.right))`
	`18`	`+`
	`19`	`+ if node.val == 3:`
	`20`	`+ node.val = bool(self.evaluateTree(node.left)) and bool(self.evaluateTree(node.right))`
	`21`	`+`
	`22`	`+ return node.val`

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	`1`	`+# lowest common ancestor in binary search tree \| leetcode 235 \| https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/`
	`2`	`+# method: iteration through each node, when p and q are in different subtrees, current node is LCA`
	`3`	`+`
	`4`	`+# Definition for a binary tree node.`
	`5`	`+class TreeNode:`
	`6`	`+ def __init__(self, x):`
	`7`	`+ self.val = x`
	`8`	`+ self.left = None`
	`9`	`+ self.right = None`
	`10`	`+`
	`11`	`+class Solution:`
	`12`	`+ def lowestCommonAncestor(self, root: 'TreeNode', p: 'TreeNode', q: 'TreeNode') -> 'TreeNode':`
	`13`	`+ cur = root`
	`14`	`+`
	`15`	`+ while cur:`
	`16`	`+ if p.val > cur.val and q.val > cur.val:`
	`17`	`+ cur = cur.right`
	`18`	`+ elif p.val < cur.val and q.val < cur.val:`
	`19`	`+ cur = cur.left`
	`20`	`+ else:`
	`21`	`+ return cur`
	`22`	`+`
	`23`	`+ return root`

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