874. Walking Robot Simulation

题目

A robot on an infinite XY-plane starts at point (0, 0) and faces north. The robot can receive one of three possible types of commands:

2: turn left 90 degrees,
1: turn right 90 degrees, or
1 <= k <= 9: move forward k units.

Some of the grid squares are obstacles. The ith obstacle is at grid point obstacles[i] = (xi, yi).

If the robot would try to move onto them, the robot stays on the previous grid square instead (but still continues following the rest of the route.)

Return the maximum Euclidean distance that the robot will be from the origin squared (i.e. if the distance is 5, return 25).

Note:

North means +Y direction.
East means +X direction.
South means -Y direction.
West means -X direction.

Example 1:

Input: commands = [4,-1,3], obstacles = []
Output: 25
Explanation: The robot starts at (0, 0):
1. Move north 4 units to (0, 4).
2. Turn right.
3. Move east 3 units to (3, 4).
The furthest point away from the origin is (3, 4), which is 32 + 42 = 25 units away.

Example 2:

Input: commands = [4,-1,4,-2,4], obstacles = [[2,4]]
Output: 65
Explanation: The robot starts at (0, 0):
1. Move north 4 units to (0, 4).
2. Turn right.
3. Move east 1 unit and get blocked by the obstacle at (2, 4), robot is at (1, 4).
4. Turn left.
5. Move north 4 units to (1, 8).
The furthest point away from the origin is (1, 8), which is 12 + 82 = 65 units away.

Constraints:

1 <= commands.length <= 104
commands[i] is one of the values in the list [-2,-1,1,2,3,4,5,6,7,8,9].
0 <= obstacles.length <= 104
3 * 104 <= xi, yi <= 3 * 104
The answer is guaranteed to be less than 231.

题目大意

机器人在一个无限大小的 XY 网格平面上行走，从点 (0, 0) 处开始出发，面向北方。该机器人可以接收以下三种类型的命令 commands ：

2 ：向左转 90 度
-1 ：向右转 90 度
1 <= x <= 9 ：向前移动 x 个单位长度

在网格上有一些格子被视为障碍物 obstacles 。第 i 个障碍物位于网格点 obstacles[i] = (xi, yi) 。机器人无法走到障碍物上，它将会停留在障碍物的前一个网格方块上，但仍然可以继续尝试进行该路线的其余部分。返回从原点到机器人所有经过的路径点（坐标为整数）的最大欧式距离的平方。（即，如果距离为 5 ，则返回 25 ）

注意：

北表示 +Y 方向。
东表示 +X 方向。
南表示 -Y 方向。
西表示 -X 方向。

解题思路

这个题的难点在于，怎么用编程语言去描述机器人的行为，可以用以下数据结构表达机器人的行为：

direct:= 0                    // direct表示机器人移动方向：0 1 2 3 4 （北东南西），默认朝北
x, y := 0, 0                  // 表示当前机器人所在横纵坐标位置，默认为(0,0)
directX := []int{0, 1, 0, -1}
directY := []int{1, 0, -1, 0}
// 组合directX directY和direct，表示机器人往某一个方向移动
nextX := x + directX[direct]
nextY := y + directY[direct]

其他代码按照题意翻译即可

代码

package leetcode

func robotSim(commands []int, obstacles [][]int) int {
	m := make(map[[2]int]struct{})
	for _, v := range obstacles {
		if len(v) != 0 {
			m[[2]int{v[0], v[1]}] = struct{}{}
		}
	}
	directX := []int{0, 1, 0, -1}
	directY := []int{1, 0, -1, 0}
	direct, x, y := 0, 0, 0
	result := 0
	for _, c := range commands {
		if c == -2 {
			direct = (direct + 3) % 4
			continue
		}
		if c == -1 {
			direct = (direct + 1) % 4
			continue
		}
		for ; c > 0; c-- {
			nextX := x + directX[direct]
			nextY := y + directY[direct]
			if _, ok := m[[2]int{nextX, nextY}]; ok {
				break
			}
			tmpResult := nextX*nextX + nextY*nextY
			if tmpResult > result {
				result = tmpResult
			}
			x = nextX
			y = nextY
		}
	}
	return result
}

Uh oh!