Python Ch1

1 files changed, 55 insertions, 0 deletions

diff --git a/challenge-064/sangeet-kar/python/ch-1.py b/challenge-064/sangeet-kar/python/ch-1.py
new file mode 100755
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+++ b/challenge-064/sangeet-kar/python/ch-1.py
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+#!/usr/bin/env python
+
+from collections import namedtuple
+import heapq
+
+Node = namedtuple('Node', 'pos, path, cost, visited')
+
+def manhattan_dist(pos, goal):
+    return goal[0] - pos[0] + goal[1] - pos[1]
+
+def next_states(pos, matrix):
+    xmax, ymax = len(matrix), len(matrix[0])
+    x, y = pos
+    return [(x1, y1) 
+            for x1, y1 in [(x-1, y), (x+1, y), (x, y+1), (x, y-1)]
+            if (0 <= x1 < xmax) and (0 <= y1 < ymax)]
+
+def move(curr_node, pos, matrix):
+    cost = matrix[pos[0]][pos[1]]
+    return Node(pos, curr_node.path + [cost], curr_node.cost + cost, curr_node.visited.union([pos]))
+
+
+def solve(matrix):
+    init = (0, 0)
+    goal = (len(matrix)-1, len(matrix[0])-1)
+
+    curr_cost = matrix[init[0]][init[1]]
+    states = [(manhattan_dist(init, goal), Node(init, [curr_cost], curr_cost, set([init])))]
+    heapq.heapify(states)
+
+    while states:
+        _, best_node = heapq.heappop(states)
+        if best_node.pos == goal:
+            print_result(best_node)
+            break
+        for state in next_states(best_node.pos, matrix):
+            next_node = move(best_node, state, matrix)
+            if not state in best_node.visited:
+                heapq.heappush(states, (next_node.cost + manhattan_dist(next_node.pos, goal),
+                                        next_node))
+
+def print_result(node):
+    print(f"Best path: {node.cost} ({'->'.join(str(p) for p in node.path)})")
+
+
+solve([[1, 2, 3],
+       [4, 5, 6],
+       [7, 8, 9]])
+
+#More complicated case
+solve([[1, 2, 3],
+       [12, 2, 6],
+       [-3, 6, 20],
+       [2, 8, 9]])
+