Merge pull request #125 from NovaHe/feature/874

feature/874: add 874 solution

Author: halfrost

leetcode/0874.Walking-Robot-Simulation/README.md

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+# [875. Koko Eating Bananas](https://leetcode.com/problems/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 ）
+
+  示例 1：
+输入：commands = [4,-1,3], obstacles = []
+输出：25
+解释：
+机器人开始位于 (0, 0)：
+1. 向北移动 4 个单位，到达 (0, 4)
+2. 右转
+3. 向东移动 3 个单位，到达 (3, 4)
+距离原点最远的是 (3, 4) ，距离为 32 + 42 = 25
+
+ 示例 2：
+输入：commands = [4,-1,4,-2,4], obstacles = [[2,4]]
+输出：65
+解释：机器人开始位于 (0, 0)：
+1. 向北移动 4 个单位，到达 (0, 4)
+2. 右转
+3. 向东移动 1 个单位，然后被位于 (2, 4) 的障碍物阻挡，机器人停在 (1, 4)
+4. 左转
+5. 向北走 4 个单位，到达 (1, 8)
+距离原点最远的是 (1, 8) ，距离为 12 + 82 = 65
+
+
+提示：
+
+- `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`.
+
+
+## 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：
+```go
+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

leetcode/0874.Walking-Robot-Simulation/Walking Robot Simulation.go

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+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
+}

leetcode/0874.Walking-Robot-Simulation/Walking Robot Simulation_test.go

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+package leetcode
+
+import "testing"
+
+func Test_robotSim(t *testing.T) {
+	type args struct {
+		commands  []int
+		obstacles [][]int
+	}
+	cases := []struct {
+		name string
+		args args
+		want int
+	}{
+		{
+			"case 1",
+			args{
+				commands:  []int{4, -1, 3},
+				obstacles: [][]int{{}},
+			},
+			25,
+		},
+		{
+			"case 2",
+			args{
+				commands:  []int{4, -1, 4, -2, 4},
+				obstacles: [][]int{{2, 4}},
+			},
+			65,
+		},
+	}
+	for _, tt := range cases {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := robotSim(tt.args.commands, tt.args.obstacles); got != tt.want {
+				t.Errorf("robotSim() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}