update

hard/403.frog-jump.go

@@ -1,34 +1,41 @@
 func canCross(stones []int) bool {
 	n := len(stones)
-	m := make(map[int]int)
+	if n == 1 {
+		return true
+	} else if n == 0 || stones[1] != 1 {
+		return false
+	}
+	m := make(map[int]bool)
 	for i := 1; i < n; i++ {
-		m[stones[i]] = i
+		if 2*stones[i-1]+1 < stones[i] {
+			return false // Pruning when the gap is too large.
+		}
+		m[stones[i]] = true
 	}
-	steps := make([][]int, n)
-	steps[0] = []int{0}
-	return dfs(stones, m, n, 0, &steps)
+	return dfs(m, stones[n-1], 1, 1)
 }
 
-func dfs(stones []int, m map[int]int, n, i int, steps *[][]int) bool {
-	if i == n-1 {
+func dfs(m map[int]bool, end, pos, jump int) bool {
+	if pos+jump+1 == end || pos+jump == end || pos+jump-1 == end {
 		return true
 	}
-	for _, l := range (*steps)[i] {
-		for j := maxInt(1, l-1); j <= l+1; j++ {
-			if idx, ok := m[stones[i]+j]; ok {
-				(*steps)[idx] = append((*steps)[idx], j)
-				if dfs(stones, m, n, idx, steps) {
-					return true
-				}
-			}
+	if _, ok := m[pos+jump+1]; ok {
+		if dfs(m, end, pos+jump+1, jump+1) {
+			return true
+		}
+	}
+	if _, ok := m[pos+jump]; ok {
+		if dfs(m, end, pos+jump, jump) {
+			return true
+		}
+	}
+	if jump == 1 { // 0 is not valid
+		return false
+	} else if _, ok := m[pos+jump-1]; ok {
+		if dfs(m, end, pos+jump-1, jump-1) {
+			return true
 		}
 	}
 	return false
 }
 
-func maxInt(x, y int) int {
-	if x < y {
-		return y
-	}
-	return x
-}

hard/407.trapping-rain-water-ii.go

@@ -0,0 +1,3 @@
+func trapRainWater(heightMap [][]int) int {
+	
+}