More chapter 8 problems

Author: StBogdan

chapter_8/p8_12.py

@@ -0,0 +1,47 @@
+from typing import List
+
+
+def queens_8():
+    current_queens = []
+    ways = 0
+    for i in range(8):
+        ways += rec_queen_place(1, [(i, 0)])
+
+    return ways
+
+
+def rec_queen_place(col: int, queen_list):
+    # print(f"Current queens {queen_list}")
+    if col >= 8:
+        display_queen_placement(queen_list)
+        return 1
+
+    possible_rows = set(range(8))
+    for (qr, qc) in queen_list:
+        possible_rows.remove(qr)
+
+    ways = 0
+    for row in possible_rows:
+        if valid_w_queens((row, col), queen_list):
+            ways += rec_queen_place(col+1, queen_list + [(row, col)])
+    return ways
+
+
+def valid_w_queens(poz, queens):
+    diag_desc = poz[0]-poz[1]
+    diag_asc = poz[0] + poz[1]
+    return not any(qi-qj == diag_desc or qi+qj == diag_asc
+                   for (qi, qj) in queens)
+
+
+def display_queen_placement(ql: List):
+    board = [['_' for _ in range(8)] for _ in range(8)]
+    for qi, qj in ql:
+        board[qi][qj] = "Q"
+
+    for line in board:
+        print(line)
+    print("-"*50)
+
+if __name__ == "__main__":
+    print(f"Got ways to put 8 queens: {queens_8()}")

chapter_8/p8_6.py

@@ -0,0 +1,33 @@
+def hanoi_towers(n):
+    stacks = [[], [], []]
+    stacks[0] = list(range(n, 0, -1))
+
+    print(f"Got start stacks\t{stacks}")
+    move_stack(n, 0, 2, stacks)
+    display_stacks(stacks)
+
+
+def move_disk(source_ind, target_ind, stacks):
+    stacks[target_ind].append(stacks[source_ind].pop())
+
+
+def display_stacks(stacks):
+    for i, stack in enumerate(stacks):
+        print(f"{i} -> {stack}")
+    print("-"*50)
+
+
+def move_stack(elem_bot, src, target, stacks):
+    display_stacks(stacks)
+    temp_stack = 3 - src - target
+    top_src = stacks[src][-1]
+    if top_src == elem_bot:
+        move_disk(src, target, stacks)
+    else:
+        move_stack(elem_bot-1, src, temp_stack, stacks)
+        move_disk(src, target, stacks)
+        move_stack(elem_bot-1, temp_stack, target, stacks)
+
+
+if __name__ == "__main__":
+    hanoi_towers(4)

chapter_8/p8_7.py

@@ -0,0 +1,28 @@
+import math
+
+def perm_uniq(inp: str):
+    return rec_perm("", inp)
+
+
+def rec_perm(prefix, ltr_pool):
+    if not ltr_pool:
+        return [prefix]
+
+    perms = []
+    for i, ltr in enumerate(ltr_pool):
+        nprefix = prefix + ltr
+        sub_perm = rec_perm(nprefix, ltr_pool[:i] + ltr_pool[i+1:])
+        perms += sub_perm
+
+    return perms
+
+
+if __name__ == "__main__":
+    exs = ["a", "", "abc", "abcd", "abcdef"]
+
+    for ex in exs:
+        permutations = perm_uniq(ex)
+        print(
+            f"Perms {len(ex)} of nr {len(permutations)}"
+            f" same as predicted {math.factorial(len(ex))}"
+            f" \t{ex} are {permutations}")

chapter_8/p8_8.py

@@ -0,0 +1,39 @@
+from collections import Counter
+from typing import List
+import math
+
+
+def perm_dups(words: str):
+    count = Counter(words)
+    res_list_list = perm_w_count(count)
+    return ["".join(res) for res in res_list_list]
+
+
+def perm_w_count(counter: dict) -> List[List]:
+    res = []
+    has_to_place = False
+
+    for k, v in counter.items():
+        if v > 0:
+            has_to_place = True
+            call_dict = counter.copy()
+            # print(f"Call dict is {call_dict}")
+            call_dict[k] -= 1
+            res_subcall = perm_w_count(call_dict)
+            res.extend([[k] + rest for rest in res_subcall])
+
+    if not has_to_place:
+        return [[""]]
+    else:
+        return res
+
+
+if __name__ == "__main__":
+    exs = ["a", "", "abc", "abcd", "aaab", "bbaa", "calalc", "aqa"]
+
+    for ex in exs:
+        permutations = perm_dups(ex)
+        print(
+            f"Perms input len: {len(ex)} of computed: {len(permutations)}"
+            f" \t{ex} are {permutations}")
+        print("-"*50)