2022-06-08

213. House Robber II

Description

You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed. All houses at this place are arranged in a circle. That means the first house is the neighbor of the last one. Meanwhile, adjacent houses have a security system connected, and it will automatically contact the police if two adjacent houses were broken into on the same night.

Given an integer array nums representing the amount of money of each house, return the maximum amount of money you can rob tonight without alerting the police.

Example 1:

Input: nums = [2,3,2]
Output: 3
Explanation: You cannot rob house 1 (money = 2) and then rob house 3 (money = 2), because they are adjacent houses.

Example 2:

Input: nums = [1,2,3,1]
Output: 4
Explanation: Rob house 1 (money = 1) and then rob house 3 (money = 3).
Total amount you can rob = 1 + 3 = 4.

Example 3:

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

Constraints:

• 1 <= nums.length <= 100

• 0 <= nums[i] <= 1000

Solution

Approach #0

func rob(nums []int) int {
    n := len(nums)
    if n == 1 {
        return nums[0]
    }
    if n == 2 {
        return max(nums[0], nums[1])
    }
    return max(_rob(nums[:n-1]), _rob(nums[1:]))
}

func _rob(nums []int) int {
    first, second := nums[0], max(nums[0], nums[1])
    for _, num := range nums[2:] {
        first, second = second, max(first+num, second)
    }
    return second
}

func max(a, b int) int {
    if a > b {
        return a
    }
    return b
}

55. Jump Game

Description

You are given an integer array nums. You are initially positioned at the array's first index, and each element in the array represents your maximum jump length at that position.

Return true if you can reach the last index, or false otherwise.

Example 1:

Input: nums = [2,3,1,1,4]
Output: true
Explanation: Jump 1 step from index 0 to 1, then 3 steps to the last index.

Example 2:

Input: nums = [3,2,1,0,4]
Output: false
Explanation: You will always arrive at index 3 no matter what. Its maximum jump length is 0, which makes it impossible to reach the last index.

Constraints:

• 1 <= nums.length <= 10^4

• 0 <= nums[i] <= 10^5

Solution

Approach #0

func canJump(nums []int) bool {
    right := 0
    for i, num := range nums {
        if i > right {
            return false
        }
        right = max(right, i+num)
        if right >= len(nums)-1 {
            return true
        }
    }
    return false
}

func max(a, b int) int {
    if a > b {
        return a
    }
    return b
}

1037. Valid Boomerang

Description

Given an array points where points[i] = [xi, yi] represents a point on the X-Y plane, return true if these points are a boomerang.

A boomerang is a set of three points that are all distinct and not in a straight line.

Example 1:

Input: points = [[1,1],[2,3],[3,2]]
Output: true

Example 2:

Input: points = [[1,1],[2,2],[3,3]]
Output: false

Constraints:

• points.length == 3

• points[i].length == 2

• 0 <= x[i], y[i] <= 100

Solution

Approach #0

func isBoomerang(points [][]int) bool {
    v1 := [2]int{points[1][0] - points[0][0], points[1][1] - points[0][1]}
    v2 := [2]int{points[2][0] - points[1][0], points[2][1] - points[1][1]}
    return v1[0]*v2[1]-v2[0]*v1[1] != 0
}