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CSES Problem Set

Visiting Cities

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CSES - Visiting Cities

Time limit:1.00 s Memory limit:512 MB

You want to travel from Syrjälä to Lehmälä by plane using a minimum-price route. Which cities will you certainly visit?


The first input line contains two integers $n$ and $m$: the number of cities and the number flights. The cities are numbered $1,2,\ldots,n$. City 1 is Syrjälä, and city $n$ is Lehmälä.

After this, there are $m$ lines that describe the flights. Each line has three integers $a$, $b$, and $c$: there is a flight from city $a$ to city $b$ with price $c$. All flights are one-way flights.


First print an integer $k$: the number of cities that are certainly in the route. After this, print the $k$ cities sorted in increasing order.


5 6
1 2 3
1 3 4
2 3 1
2 4 5
3 4 1
4 5 8

1 3 4 5