go: add «2751. Robot Collisions»

Signed-off-by: Matej Focko <me@mfocko.xyz>

go/robot-collisions.go

@@ -0,0 +1,71 @@
+package main
+
+import (
+	"cmp"
+	"slices"
+)
+
+type Robot struct {
+	index     int
+	position  int
+	health    int
+	direction byte
+}
+
+func survivedRobotsHealths(positions []int, healths []int, directions string) []int {
+	// construct a slice of robots instead of separate slices
+	robots := make([]Robot, len(positions))
+	for i := range len(positions) {
+		robots[i] = Robot{
+			index:     i,
+			position:  positions[i],
+			health:    healths[i],
+			direction: directions[i],
+		}
+	}
+
+	// sort by positions
+	slices.SortFunc(robots, func(a, b Robot) int {
+		return cmp.Compare(a.position, b.position)
+	})
+
+	var stack []*Robot
+	for i := range robots {
+		robot := &robots[i]
+		if robot.direction == 'R' {
+			stack = append(stack, robot)
+			continue
+		}
+
+		for len(stack) > 0 && robot.health > 0 {
+			otherRobot := stack[len(stack)-1]
+			stack = stack[:len(stack)-1]
+
+			if otherRobot.health > robot.health {
+				otherRobot.health--
+				robot.health = 0
+				stack = append(stack, otherRobot)
+			} else if otherRobot.health < robot.health {
+				robot.health--
+				otherRobot.health = 0
+			} else {
+				robot.health = 0
+				otherRobot.health = 0
+			}
+		}
+	}
+
+	// revert to the original ordering to preserve the order of the robots
+	// for the output
+	slices.SortFunc(robots, func(a, b Robot) int {
+		return cmp.Compare(a.index, b.index)
+	})
+
+	var hp []int
+	for _, robot := range robots {
+		if robot.health > 0 {
+			hp = append(hp, robot.health)
+		}
+	}
+	return hp
+}