add new solutions

solutions/7/q714/solution.go

@@ -0,0 +1,33 @@
+package q714
+
+// Note: could be done faster with dynamic programming
+
+func maxProfit(prices []int, fee int) int {
+	var low, high, profit int
+	bought := false
+	for i := range prices {
+		if bought {
+			high = max(high, prices[i])
+			if high-prices[i] > fee { // should have sold earlier or not bought
+				if high-low > fee {
+					profit += high - low - fee
+				}
+				bought = false
+			} else if prices[i] < low { // regret buying too early
+				low, high = prices[i], prices[i]
+			}
+		}
+
+		if !bought && i < len(prices)-1 && prices[i+1] > prices[i] {
+			bought = true // buy the dip
+			low, high = prices[i], prices[i]
+		}
+	}
+
+	if bought && high-low > fee {
+		profit += high - low - fee
+	}
+	return profit
+}
+
+var _ = maxProfit

solutions/7/q735/solution.go

@@ -0,0 +1,23 @@
+package q735
+
+func asteroidCollision(asteroids []int) []int {
+	p := 0
+	for _, a := range asteroids {
+		if a < 0 {
+			for p > 0 && asteroids[p-1] > 0 && asteroids[p-1] < -a {
+				p--
+			}
+			if p > 0 && asteroids[p-1] > 0 {
+				if asteroids[p-1] == -a {
+					p--
+				}
+				continue // explode
+			}
+		}
+		asteroids[p] = a
+		p++
+	}
+	return asteroids[:p]
+}
+
+var _ = asteroidCollision

solutions/7/q739/solution.go

@@ -0,0 +1,19 @@
+package q739
+
+func dailyTemperatures(temperatures []int) []int {
+	waitDays := make([]int, len(temperatures))
+
+	idxStack := make([]int, 0, len(temperatures))
+	for i, temp := range temperatures {
+		for len(idxStack) > 0 && temperatures[idxStack[len(idxStack)-1]] < temp {
+			popped := idxStack[len(idxStack)-1]
+			idxStack = idxStack[:len(idxStack)-1] // pop
+
+			waitDays[popped] = i - popped
+		}
+		idxStack = append(idxStack, i)
+	}
+	return waitDays
+}
+
+var _ = dailyTemperatures

solutions/7/q790/solution.go

@@ -0,0 +1,24 @@
+package q790
+
+const (
+	TopHalf int8 = iota
+	BottomHalf
+	Full
+
+	Modulo int = 1e9 + 7
+)
+
+func numTilings(n int) int {
+	cache := make([][3]int, n+1)
+	cache[0][Full] = 1
+	cache[1][Full] = 1
+
+	for w := 2; w <= n; w++ {
+		cache[w][Full] = (cache[w-1][Full] + cache[w-2][Full] + cache[w-1][TopHalf] + cache[w-1][BottomHalf]) % Modulo
+		cache[w][TopHalf] = (cache[w-1][BottomHalf] + cache[w-2][Full]) % Modulo
+		cache[w][BottomHalf] = (cache[w-1][TopHalf] + cache[w-2][Full]) % Modulo
+	}
+	return cache[n][Full]
+}
+
+var _ = numTilings