골목 대장 호석 풀이

Author: saebyeok0306

BAEKJOON/3Gold/골목 대장 호석.py

@@ -0,0 +1,69 @@
+# 그래프 이론, 이분 탐색, 최단 경로, 데이크스트라, 매개 변수 탐색
+# https://www.acmicpc.net/problem/20183
+
+"""
+5 5 1 3 10
+1 2 5
+2 3 5
+1 4 1
+4 5 6
+5 3 1
+"""
+
+input = __import__("sys").stdin.readline
+
+N,M,A,B,C = map(int, input().split())
+graph = [[] for _ in range(N+1)]
+costs = []
+for _ in range(M):
+    a,b,c = map(int, input().split())
+    graph[a].append((b,c))
+    graph[b].append((a,c))
+    costs.append(c)
+
+costs.sort()
+
+INF = int(1e15)
+
+def dijkstra(limit_cost):
+    import heapq
+
+    heap = [(0,A)] # 비용, 노드
+    dist = [INF]*(N+1) # 비용
+    dist[A] = 0
+
+    while heap:
+        cost, node = heapq.heappop(heap)
+
+        if dist[node] < cost:
+            continue
+
+        for nxt_node, nxt_cost in graph[node]:
+            sum_cost = dist[node] + nxt_cost
+
+            if limit_cost < nxt_cost:
+                continue
+
+            if sum_cost > C or dist[nxt_node] <= sum_cost:
+                continue
+
+            dist[nxt_node] = sum_cost
+
+            heapq.heappush(heap, (sum_cost, nxt_node))
+    
+    return dist[B]
+
+l = 0
+r = M-1
+answer = INF
+
+while l <= r:
+    mid = (l+r)//2
+    cost = dijkstra(costs[mid])
+    if cost == INF:
+        l = mid+1
+    else:
+        r = mid-1
+        answer = min(costs[mid], answer)
+
+print(-1 if answer == INF else answer)