Jump game finally (?) but differently than solutions

leetcode/stuff.py

@@ -328,18 +328,6 @@ class JumpSpace(typing.NamedTuple):
         return ret
 
 
-def count_min_jumps_from_board(board: list[int]) -> int:
-    if len(board) == 1:
-        return 0
-
-    complete_paths = collect_complete_jump_paths_from_board(board)
-
-    if len(complete_paths) == 0:
-        return -1
-
-    return min([len(p) - 1 for p in complete_paths])
-
-
 def collect_complete_jump_paths_from_board(board: list[int]) -> list[list[int]]:
     return [
         p
@@ -354,3 +342,42 @@ def collect_jump_paths_from_board(board: list[int]) -> list[list[int]]:
         return []
 
     return space.jump_paths()
+
+
+# NOTE: the expensive way goes like this
+# complete_paths = collect_complete_jump_paths_from_board(board)
+
+# if len(complete_paths) == 0:
+#     return -1
+
+# return min([len(p) - 1 for p in complete_paths])
+
+
+def count_min_jumps_from_board(board: list[int]) -> int:
+    return len(collect_min_jumps_from_board(board))
+
+
+def collect_min_jumps_from_board(board: list[int]) -> list[int]:
+    if len(board) < 3:
+        return list(range(1, len(board)))
+
+    jumps: list[int] = []
+    range_begin: int = 0
+    val = board[range_begin]
+    range_end: int = range_begin + val + 1
+
+    while range_end < len(board):
+        potential_jumps = board[range_begin:range_end]
+
+        scored_jumps = [
+            (val + range_begin + i, val, range_begin + i)
+            for i, val in enumerate(potential_jumps)
+        ]
+        _, val, space = max(scored_jumps)
+
+        jumps.append(space)
+
+        range_begin = space
+        range_end = range_begin + val + 1
+
+    return jumps + [len(board) - 1]