オムロンプログラミングコンテスト2025(AtCoder Beginner Contest 397)
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Problem Statement
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You are given a directed graph with $N$ vertices and $M$ edges. The vertices are numbered $1,2,\dots,N$. Edge $j$ ($j=1,2,\dots,M$) goes from vertex $u_j$ to vertex $v_j$. It is guaranteed that vertex $N$ is reachable from vertex $1$.
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Initially, all edges have weight $0$. We choose exactly $K$ out of the $M$ edges and change their weights to $1$. Find the maximum possible value of the shortest distance from vertex $1$ to vertex $N$ in the resulting graph.
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Constraints
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$2 \leq N \leq 30$$1 \leq K \leq M \leq 100$$1 \leq u_j, v_j \leq N$$u_j \neq v_j$- In the given graph, vertex
$N$is reachable from vertex$1$. - All input values are integers.
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Input
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The input is given from Standard Input in the following format:
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N M K
u_1 v_1
u_2 v_2
\vdots
u_M v_M
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Output
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Print the answer.
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样例
Input #1
3 3 2
1 2
2 3
1 3
Output #1
1
By choosing edges $1,3$, the shortest distance from vertex $1$ to vertex $3$ becomes $1$. There is no way to make the shortest distance $2$ or greater, so the answer is $1$.
Input #2
4 4 3
1 2
1 3
3 2
2 4
Output #2
2
By choosing edges $1,2,4$, the shortest distance from vertex $1$ to vertex $4$ becomes $2$. There is no way to make the shortest distance $3$ or greater, so the answer is $2$.
Input #3
2 2 1
1 2
1 2
Output #3
0
Note that there may be multi-edges.
题目信息
题面与样例版权归 AtCoder 及出题人所有;中文翻译由 AI 生成(CI 管线),如有出入请以原文为准。