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BST Problems
/**
* Definition for a binary tree node.
* type TreeNode struct {
* Val int
* Left *TreeNode
* Right *TreeNode
* }
*/
func dfs(node *TreeNode, path string, paths *[]string) {
if node == nil {
return
}
val := strconv.Itoa(node.Val)
if path != "" {
val = path + "->" + val
}
if node.Left == nil && node.Right == nil {
*paths = append(*paths, val)
return
}
dfs(node.Left, val, paths)
dfs(node.Right, val, paths)
}
func binaryTreePaths(root *TreeNode) []string {
paths := make([]string, 0)
dfs(root, "", &paths)
return paths
}
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, val=0, left=None, right=None):
# self.val = val
# self.left = left
# self.right = right
def dfs(node, level, res):
if node.left is None and node.right is None:
res.append((node.val, level))
if node.left:
dfs(node.left, level + 1, res)
if node.right:
dfs(node.right, level + 1, res)
class Solution:
def deepestLeavesSum(self, root: TreeNode) -> int:
res = []
dfs(root, 0, res)
max_level = 0
for (v, level) in res:
max_level = max(max_level, level)
result = 0
for (v, level) in res:
if level == max_level:
result += v
return result
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, val=0, left=None, right=None):
# self.val = val
# self.left = left
# self.right = right
def dfs(node, level):
ll = 0
lr = 0
if node.left is not None:
ll = dfs(node.left, level + 1)
if node.right is not None:
lr = dfs(node.right, level + 1)
return max(ll, lr, level)
class Solution:
def maxDepth(self, root: TreeNode) -> int:
if not root:
return 0
return dfs(root, 1)
DIRS = [(0, 1), (1, 0), (-1, 0), (0, -1)]
def dfs(grid, i, j):
grid[i][j] = '0'
for (ix, jx) in DIRS:
ni, nj = i + ix, j + jx
if ni < 0 or nj < 0 or ni >= len(grid) or nj >= len(grid[ni]):
continue
if grid[ni][nj] == '0':
continue
dfs(grid, ni, nj)
class Solution:
def numIslands(self, grid: List[List[str]]) -> int:
res = 0
for i in range(len(grid)):
for j in range(len(grid[i])):
if grid[i][j] == '1':
res += 1
dfs(grid, i, j)
return res
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