Merge pull request #659 from 0xff-dev/2731

Add solution and test-cases for problem 2731

leetcode/2701-2800/2731.Movement-of-Robots/README.md

@@ -0,0 +1,51 @@
+# [2731. Movement of Robots][title]
+
+## Description
+Some robots are standing on an infinite number line with their initial coordinates given by a **0-indexed** integer array `nums` and will start moving once given the command to move. The robots will move a unit distance each second.
+
+You are given a string `s` denoting the direction in which robots will move on command. `'L'` means the robot will move towards the left side or negative side of the number line, whereas `'R'` means the robot will move towards the right side or positive side of the number line.
+
+If two robots collide, they will start moving in opposite directions.
+
+Return the sum of distances between all the pairs of robots `d` seconds after the command. Since the sum can be very large, return it modulo `10^9 + 7`.
+
+**Note:**
+
+- For two robots at the index `i` and `j`, pair (`i,j`) and pair (`j,i`) are considered the same pair.
+- When robots collide, they **instantly change** their directions without wasting any time.
+- Collision happens when two robots share the same place in a moment.
+    - For example, if a robot is positioned in 0 going to the right and another is positioned in 2 going to the left, the next second they'll be both in 1 and they will change direction and the next second the first one will be in 0, heading left, and another will be in 2, heading right.
+    - For example, if a robot is positioned in 0 going to the right and another is positioned in 1 going to the left, the next second the first one will be in 0, heading left, and another will be in 1, heading right.
+
+**Example 1:**
+
+```
+Input: nums = [-2,0,2], s = "RLL", d = 3
+Output: 8
+Explanation: 
+After 1 second, the positions are [-1,-1,1]. Now, the robot at index 0 will move left, and the robot at index 1 will move right.
+After 2 seconds, the positions are [-2,0,0]. Now, the robot at index 1 will move left, and the robot at index 2 will move right.
+After 3 seconds, the positions are [-3,-1,1].
+The distance between the robot at index 0 and 1 is abs(-3 - (-1)) = 2.
+The distance between the robot at index 0 and 2 is abs(-3 - 1) = 4.
+The distance between the robot at index 1 and 2 is abs(-1 - 1) = 2.
+The sum of the pairs of all distances = 2 + 4 + 2 = 8.
+```
+
+**Example 2:**
+
+```
+Input: nums = [1,0], s = "RL", d = 2
+Output: 5
+Explanation: 
+After 1 second, the positions are [2,-1].
+After 2 seconds, the positions are [3,-2].
+The distance between the two robots is abs(-2 - 3) = 5.
+```
+
+## 结语
+
+如果你同我一样热爱数据结构、算法、LeetCode，可以关注我 GitHub 上的 LeetCode 题解：[awesome-golang-algorithm][me]
+
+[title]: https://leetcode.com/problems/movement-of-robots
+[me]: https://github.com/kylesliu/awesome-golang-algorithm

leetcode/2701-2800/2731.Movement-of-Robots/Solution.go

@@ -1,5 +1,62 @@
 package Solution
 
-func Solution(x bool) bool {
-	return x
+import (
+	"sort"
+)
+
+const mod2731 = 1000000007
+
+func Solution(nums []int, s string, d int) int {
+
+	length := len(nums)
+	for i := range nums {
+		if s[i] == 'R' {
+			nums[i] += d
+			continue
+		}
+		nums[i] -= d
+	}
+	sort.Ints(nums)
+
+	sum := make([][]int, length)
+	for i := len(nums) - 1; i >= 0; i-- {
+		sum[i] = make([]int, 4)
+		if i == len(nums)-1 {
+			if nums[i] < 0 {
+				sum[i][0] = nums[i]
+				sum[i][1] = 1
+			} else {
+				sum[i][2] = nums[i]
+				sum[i][3] = 1
+			}
+			continue
+		}
+		if nums[i] < 0 {
+			sum[i][0] = sum[i+1][0] + nums[i]
+			sum[i][1] = sum[i+1][1] + 1
+			sum[i][2] = sum[i+1][2]
+			sum[i][3] = sum[i+1][3]
+		} else {
+			sum[i][2] = sum[i+1][2] + nums[i]
+			sum[i][3] = sum[i+1][3] + 1
+			sum[i][0] = sum[i+1][0]
+			sum[i][1] = sum[i+1][1]
+		}
+	}
+	ans := 0
+	var a, b int
+	for i := 0; i < length-1; i++ {
+		a = nums[i]*sum[i+1][3] - sum[i+1][2]
+		b = nums[i]*sum[i+1][1] - sum[i+1][0]
+		if a < 0 {
+			a = -a
+		}
+		if b < 0 {
+			b = -b
+		}
+		a += b
+
+		ans = (ans + a) % mod2731
+	}
+	return ans
 }

leetcode/2701-2800/2731.Movement-of-Robots/Solution_test.go

@@ -10,30 +10,31 @@ func TestSolution(t *testing.T) {
 	//	测试用例
 	cases := []struct {
 		name   string
-		inputs bool
-		expect bool
+		nums   []int
+		s      string
+		d      int
+		expect int
 	}{
-		{"TestCase", true, true},
-		{"TestCase", true, true},
-		{"TestCase", false, false},
+		{"TestCase1", []int{-2, 0, 2}, "RLL", 3, 8},
+		{"TestCase2", []int{1, -67, 68, -26, -13, -40, -56, 62, 21}, "LLLRLLRRR", 4, 2106},
 	}
 
 	//	开始测试
 	for i, c := range cases {
 		t.Run(c.name+" "+strconv.Itoa(i), func(t *testing.T) {
-			got := Solution(c.inputs)
+			got := Solution(c.nums, c.s, c.d)
 			if !reflect.DeepEqual(got, c.expect) {
-				t.Fatalf("expected: %v, but got: %v, with inputs: %v",
-					c.expect, got, c.inputs)
+				t.Fatalf("expected: %v, but got: %v, with inputs: %v %v %v",
+					c.expect, got, c.nums, c.s, c.d)
 			}
 		})
 	}
 }
 
-//	压力测试
+// 压力测试
 func BenchmarkSolution(b *testing.B) {
 }
 
-//	使用案列
+// 使用案列
 func ExampleSolution() {
 }