The beaver community is designing a new dam on the river. They want to use the least number of logs. They are clever, so they want to take advantage of the small islands in the river. The picture shows the river, the islands, and the number of logs needed to build each dam segment.
河狸们正在河上设计一座新水坝。它们想用最少的原木。它们很聪明，所以想利用河中的小岛。图中展示了河流、小岛以及建造每段水坝所需的原木数量。
You can add a log to the beavers' design by clicking on a log in the picture
您可以通过点击图片中的原木，向海狸的设计中添加一根原木。
To remove a log, click on the log again.
要删除一条日志，请再次点击该日志。
The total number of logs needed for the dam is shown at the top.
大坝所需的原木总数显示在顶部。
Question: 问题:
What is the least number of logs needed for the new dam?
建造新水坝至少需要多少根原木？
Click Save answer when you think you have found it.
当你认为自己找到了答案时，请点击“保存答案”。
Explanation 解释
Here is the most efficient dam design:
以下是最高效的水坝设计方案：
The beavers will need 4+4+3+4=15 logs.
海狸们将需要 4×4×3×4=15 根原木。
If you are not new to Bebras, you must had seen tasks in which you have to find the shortest path between two points. Building a dam with the the least number of logs is the same as finding the shortest path from one side of the river to another, where the length of the path segments is measured by the number of logs.
如果您对“贝瓦斯”（Bebras）并不陌生，您一定见过这样的任务：在两点之间找到最短路径。用最少数量的原木建造一座水坝，这与从河的一边到另一边找到最短路径是一样的，只不过路径段的长度是以原木的数量来衡量的。
How do we systematically find the shortest path?
我们如何系统地找到最短路径？
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