2022-05-30

82. Remove Duplicates from Sorted List II

Description

Given the head of a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list. Return the linked list sorted as well.

Example 1:

Input: head = [1,2,3,3,4,4,5]
Output: [1,2,5]

Example 2:

Input: head = [1,1,1,2,3]
Output: [2,3]

Constraints:

• The number of nodes in the list is in the range [0, 300].

• -100 <= Node.val <= 100

• The list is guaranteed to be sorted in ascending order.

Solution

Approach #0

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func deleteDuplicates(head *ListNode) *ListNode {
    return dfs(head, -101)
}

func dfs(cur *ListNode, val int) *ListNode {
    if cur == nil {
        return nil
    }
    if cur.Val == val || (cur.Next != nil && cur.Next.Val == cur.Val) {
        return dfs(cur.Next, cur.Val)
    }
    cur.Next = dfs(cur.Next, cur.Val)
    return cur
}

Approach #1

/**
 * Definition for singly-linked list.
 * type ListNode struct {
 *     Val int
 *     Next *ListNode
 * }
 */
func deleteDuplicates(head *ListNode) *ListNode {
    if head == nil {
        return nil
    }
    newHead := &ListNode{Next: head}
    cur := newHead
    for cur.Next != nil && cur.Next.Next != nil {
        if cur.Next.Val == cur.Next.Next.Val {
            v := cur.Next.Val
            for cur.Next != nil && cur.Next.Val == v {
                cur.Next = cur.Next.Next
            }
        } else {
            cur = cur.Next
        }
    }
    return newHead.Next
}

15. 3Sum

Description

Given an integer array nums, return all the triplets [nums[i], nums[j], nums[k]] such that i != j, i != k, and j != k, and nums[i] + nums[j] + nums[k] == 0.

Notice that the solution set must not contain duplicate triplets.

Example 1:

Input: nums = [-1,0,1,2,-1,-4]
Output: [[-1,-1,2],[-1,0,1]]

Example 2:

Input: nums = []
Output: []

Example 3:

Input: nums = [0]
Output: [] 

Constraints:

• 0 <= nums.length <= 3000

• -10^5 <= nums[i] <= 10^5

Solution

Approach #0

func threeSum(nums []int) [][]int {
    sort.Ints(nums)
    n := len(nums)
    var res [][]int
    for i := 0; i < n; i++ {
        if i > 0 && nums[i] == nums[i-1] {
            continue
        }
        k := n - 1
        for j := i + 1; j < n; j++ {
            if j > i+1 && nums[j] == nums[j-1] {
                continue
            }
            for j < k && nums[i]+nums[j]+nums[k] > 0 {
                k--
            }
            if j == k {
                break
            }
            if nums[i]+nums[j]+nums[k] == 0 {
                res = append(res, []int{nums[i], nums[j], nums[k]})
            }
        }
    }
    return res
}

1022. Sum of Root To Leaf Binary Numbers

Description

You are given the root of a binary tree where each node has a value 0 or 1. Each root-to-leaf path represents a binary number starting with the most significant bit.

• For example, if the path is 0 -> 1 -> 1 -> 0 -> 1, then this could represent 01101 in binary, which is 13.

For all leaves in the tree, consider the numbers represented by the path from the root to that leaf. Return the sum of these numbers.

The test cases are generated so that the answer fits in a 32-bits integer.

Example 1:

Input: root = [1,0,1,0,1,0,1]
Output: 22
Explanation: (100) + (101) + (110) + (111) = 4 + 5 + 6 + 7 = 22

Example 2:

Input: root = [0]
Output: 0 

Constraints:

• The number of nodes in the tree is in the range [1, 1000].

• Node.val is 0 or 1.

Solution

Approach #0

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func sumRootToLeaf(root *TreeNode) int {
    return sum(root, 0)
}

func sum(node *TreeNode, num int) int {
    if node.Left != nil && node.Right != nil {
        return sum(node.Left, num<<1+node.Val) + sum(node.Right, num<<1+node.Val)
    }
    if node.Left != nil {
        return sum(node.Left, num<<1+node.Val)
    }
    if node.Right != nil {
        return sum(node.Right, num<<1+node.Val)
    }
    return num<<1 + node.Val
}

Approach #1

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func sumRootToLeaf(root *TreeNode) int {
    var val, res int
    var stack []*TreeNode
    var pre *TreeNode
    for root != nil || len(stack) > 0 {
        for root != nil {
            val = val<<1 | root.Val
            stack = append(stack, root)
            root = root.Left
        }
        root = stack[len(stack)-1]
        if root.Right == nil || root.Right == pre {
            if root.Left == nil && root.Right == nil {
                res = res + val
            }
            val = val >> 1
            stack = stack[:len(stack)-1]
            pre = root
            root = nil
        } else {
            root = root.Right
        }
    }
    return res
}