daily

Author: Zanger67

my-submissions/m2976.py

@@ -0,0 +1,47 @@
+class Solution:
+    def minimumCost(self, 
+                    source: str, 
+                    target: str, 
+                    original: List[str], 
+                    changed: List[str], 
+                    cost: List[int]) -> int:
+
+        # Create mapping of each letter to their cheapest counterparts
+        conversions = [{} for _ in range(26)]
+        for o, n, c in zip(original, changed, cost) :
+            if o == n :
+                continue
+            if (ord(n) - ord('a')) not in conversions[ord(o) - ord('a')] \
+                or conversions[ord(o) - ord('a')][ord(n) - ord('a')] > c :
+                conversions[ord(o) - ord('a')][ord(n) - ord('a')] = c
+
+        # Propogate from each point to find all reachable characters
+        # and calculate the min cost using Diskstras and a heap.
+        for i in range(26) :
+            # schema: (cost, target)
+            hp = [(c, x) for x, c in conversions[i].items()]
+            heapq.heapify(hp)
+
+            while hp :
+                c, x = heapq.heappop(hp)
+                if x not in conversions[i] or c <= conversions[i][x] :
+                    conversions[i][x] = c
+
+                    # from x to target at newCost
+                    for tar, newCost in conversions[x].items() :
+                        if tar not in conversions[i] \
+                            or newCost + c <= conversions[i][tar] :
+                            heapq.heappush(hp, (newCost + c, tar))
+
+        # Iterate through the starting string and use the previously
+        # computed path-cost mapping to calculate cost
+        tot_cost = 0
+        for o, c in zip(source, target) :
+            if o == c :
+                continue
+            elif (ord(c) - ord('a')) not in conversions[ord(o) - ord('a')] :
+                return -1
+            else :
+                tot_cost += conversions[ord(o) - ord('a')].get(ord(c) - ord('a'))
+
+        return tot_cost