1488: sol with BS

Signed-off-by: ductnn <[email protected]>

Author: ductnn

leetcode/daily/1488/sol.go

@@ -0,0 +1,55 @@
+package main
+
+import (
+	"fmt"
+	"sort"
+)
+
+func avoidFlood(rains []int) []int {
+	n := len(rains)
+	ans := make([]int, n)
+	full := make(map[int]int)
+	dryDays := []int{}
+
+	for i, lake := range rains {
+		// Rain Day
+		if lake > 0 {
+			ans[i] = -1
+			if day, ok := full[lake]; ok {
+				// Lake full, need 1 dry day to dry it
+				idx := findDryDayAfter(dryDays, day) // idx in dryDays slice
+				if idx == -1 {
+					return []int{} // No dry day found -> flood
+				}
+				// Use the actual dry day (value), not the index
+				actualDay := dryDays[idx]
+				ans[actualDay] = lake
+				// Remove the used dry day from the list (by index)
+				dryDays = append(dryDays[:idx], dryDays[idx+1:]...)
+			}
+			full[lake] = i
+		} else {
+			// Dry Day
+			dryDays = append(dryDays, i)
+			ans[i] = 1
+		}
+	}
+
+	return ans
+}
+
+// Find the index in dryDays of the first day > day
+// Ex: dryDays = [2, 4, 5], day = 3 => idx = 1
+// Ex: dryDays = [2, 4, 5], day = 6 => idx = -1
+func findDryDayAfter(dryDays []int, day int) int {
+	idx := sort.Search(len(dryDays), func(i int) bool { return dryDays[i] > day })
+	if idx == len(dryDays) {
+		return -1
+	}
+	return idx
+}
+
+func main() {
+	rains := []int{1, 2, 0, 0, 2, 1}
+	fmt.Println(avoidFlood(rains)) // => [-1 -1 2 1 -1 -1]
+}