Airplane fuel-efficiency

This is a discussion on Airplane fuel-efficiency within the C Programming forums, part of the General Programming Boards category; Just for fun I figured I'd solve the problem outlined here Here's my solution: Code: #include <stdio.h> #include <stdlib.h> #define ...

  1. #1
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    Airplane fuel-efficiency

    Just for fun I figured I'd solve the problem outlined here

    Here's my solution:
    Code:
    #include <stdio.h>
    #include <stdlib.h>
    
    #define VCRUISE   400
    #define AOPT       30
    #define GPHOPT   2000
    #define GPHEXTRA   10
    #define CLIMBCOST  50
    
    double tailwind(int altitude, int tail20, int tail40)
    {
      double windinc;
    
      windinc = ((double)tail40 - tail20) / 20;
      altitude -= 20;
    
      return tail20 + windinc * altitude;
    }
    
    int climbcost(int climb)
    {
      return climb * CLIMBCOST;
    }
    
    double planespeed(double tailwind)
    {
      return VCRUISE + tailwind;
    }
    
    double legtime(int tailwind, int leglen)
    {
      return leglen / planespeed(tailwind);
    }
    
    int fuelconsumphour(int altitude)
    {
      int altdiff;
    
      altdiff = AOPT - altitude;
      if(altdiff < 0)
         altdiff = -altdiff;
    
      return GPHOPT + (GPHEXTRA * altdiff);
    }
    
    double fuelconsumpleg(int altitude, double ltime)
    {
      return climbcost(altitude) + fuelconsumphour(altitude) * ltime;
    }
    
    int main(void)
    {
      struct
      {
        int altitude;
        double fuelcost;
      } legs[10];
      char buf[4096];
      int nflights, nlegs;
      int leglen, tail20, tail40;
      int altitude;
      double wind, legfuel, flightfuel, ltime;
      int i, j;
    
      fgets(buf, sizeof(buf), stdin);
      nflights = atoi(buf);
    
      for(i = 0;i < nflights;++i)
      {
        fgets(buf, sizeof(buf), stdin);
        nlegs = atoi(buf);
    
        for(j = 0;j < nlegs;++j)
        {
          fgets(buf, sizeof(buf), stdin);
          sscanf(buf, "%d %d %d", &leglen, &tail20, &tail40);
    
          for(altitude = 20;altitude <= 40;++altitude)
          {
            wind = tailwind(altitude, tail20, tail40);
            ltime = legtime(wind, leglen);
            legfuel = fuelconsumpleg(altitude, ltime);
    
            if(altitude == 20 || legfuel < legs[j].fuelcost)
            {
              legs[j].altitude = altitude;
              legs[j].fuelcost = legfuel;
            }
          }
        }
    
        printf("Flight %d: ", i+1);
        for(flightfuel = 0, j = 0;j < nlegs;++j)
        {
          printf("%d ", legs[j].altitude);
          flightfuel += legs[j].fuelcost;
        }
        printf("%.0f\n", flightfuel);
      }
    
      return 0;
    }
    For their test data I get this:
    Code:
    Flight 1: 35 20 15235
    Flight 2: 20 30 30 26002
    instead of what they get:
    Code:
    Flight 1: 35 30 13985
    Flight 2: 20 30 40 23983
    I can't seem to find what I'm doing wrong. I blame the fact that it's Monday. I tried some debugging. I threw a printf() in the middle of the altitude loop, but it looks right and the calculations add up. I'm beginning to think I'm misunderstanding the instructions, but I can't find my fault there either.

    Anyone see what I'm missing?
    Last edited by itsme86; 01-31-2005 at 03:38 PM.
    If you understand what you're doing, you're not learning anything.

  2. #2
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    Quote Originally Posted by itsme86
    Just for fun I figured I'd solve the problem outlined here


    For their test data I get this:
    Code:
    Flight 1: 35 20 15235
    Flight 2: 20 30 30 26002
    instead of what they get:
    Code:
    Flight 1: 35 30 13985
    Flight 2: 20 30 40 23983
    I can't seem to find what I'm doing wrong. I blame the fact that it's Monday. I tried some debugging. I threw a printf() in the middle of the altitude loop, but it looks right and the calculations add up. I'm beginning to think I'm misunderstanding the instructions, but I can't find my fault there either.

    Anyone see what I'm missing?
    Maybe each leg starts at the altitude of the previous leg (that is, the individual legs represent course changes or other corrections, not new landings and takeoffs).

    Look at flight #1:

    At the end of leg 1, the plane is at 35,000 feet. Since this is above the optimum altitude, and there is no penalty for going down to the optimum altitude (and there is no tailwind for the second leg), it is "obvious" that the best altitude for leg #2 is 30,000 ft. Your program calculates the climb penalty for leg 2 from 0 feet altitude , not from the altitude at the end of leg 1.

    Worth considering?

    Regards,

    Dave
    Last edited by Dave Evans; 01-31-2005 at 11:07 PM.

  3. #3
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    I'd have to agree with Dave on this one. After making a few changes to your code, I came up with some numbers that looked closer to their sample output. I don't think I'm calculating anything incorrectly, though.
    Code:
    //changes
    int climbcost(int climb)
    {
        return (climb > 0 ? climb * CLIMBCOST : 0);
    }
    
    double fuelconsumpleg(int start_altitude, int end_altitude, double ltime)
    {
      return climbcost(end_altitude - start_altitude) + fuelconsumphour(end_altitude) * ltime;
    }
    
    //in main
    //...snip
          for(altitude = 20;altitude <= 40;++altitude)
          {
            wind = tailwind(altitude, tail20, tail40);
            ltime = legtime((int)wind, leglen);
    
            //first leg is from altitude 0, subsequent legs are from previous leg altitude
            legfuel = fuelconsumpleg((j == 0 ? 0 : legs[j-1].altitude), altitude, ltime);
    
            if(altitude == 20 || legfuel < legs[j].fuelcost)
            {
              legs[j].altitude = altitude;
              legs[j].fuelcost = legfuel;
            }
          }
    //...snip
    Code:
    //input
    2
    2
    1500 -50 50
    1000 0 0
    3
    1000 50 0
    2000 0 20
    1800 50 100
    Code:
    //Output
    Flight 1: 35 30 13985
    Flight 2: 20 30 30 23502
    It looks like a better route than the one the sample output suggests, but I could have made a logical error in calculation.
    If I did your homework for you, then you might pass your class without learning how to write a program like this. Then you might graduate and get your degree without learning how to write a program like this. You might become a professional programmer without knowing how to write a program like this. Someday you might work on a project with me without knowing how to write a program like this. Then I would have to do you serious bodily harm. - Jack Klein

  4. #4
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    Brilliant! Thank you. With the new calculations it almost works correctly. Flight 2 is still a bit off, but I can probably find the problem now.

    EDIT: pianorain, I get the exact same output with mine.
    If you understand what you're doing, you're not learning anything.

  5. #5
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    After a bit of modification, it's simple to check their output and see that it's the incorrect answer.
    Code:
    int main(void)
    {
      struct
      {
        int altitude;
        double fuelcost;
      } legs[10];
      char buf[4096];
      int nflights, nlegs;
      int leglen, tail20, tail40;
      int altitude;
      double wind, legfuel, flightfuel, ltime;
      int i, j;
    
      fgets(buf, sizeof(buf), stdin);
      nflights = atoi(buf);
    
      for(i = 0;i < nflights;++i)
      {
        fgets(buf, sizeof(buf), stdin);
        nlegs = atoi(buf);
    
        for(j = 0;j < nlegs;++j)
        {
          fgets(buf, sizeof(buf), stdin);
          sscanf(buf, "%d %d %d %d", &leglen, &tail20, &tail40, &altitude);
    
            wind = tailwind(altitude, tail20, tail40);
            ltime = legtime((int)wind, leglen);
            legfuel = fuelconsumpleg((j == 0 ? 0 : legs[j-1].altitude), altitude, ltime);
    
              legs[j].altitude = altitude;
              legs[j].fuelcost = legfuel;
        }
    
        printf("Flight %d: ", i+1);
        for(flightfuel = 0, j = 0;j < nlegs;++j)
        {
          printf("%d ", legs[j].altitude);
          flightfuel += legs[j].fuelcost;
        }
        printf("%.0f\n", flightfuel);
      }
    
      return 0;
    }
    Code:
    //input
    2
    3
    1000 50 0 20
    2000 0 20 30
    1800 50 100 30
    3
    1000 50 0 20
    2000 0 20 30
    1800 50 100 40
    Code:
    //output
    Flight 1: 20 30 30 23502
    Flight 2: 20 30 40 23983
    As you can see, itsme86, your program generates the correct answer. The sample output on the site is incorrect.
    If I did your homework for you, then you might pass your class without learning how to write a program like this. Then you might graduate and get your degree without learning how to write a program like this. You might become a professional programmer without knowing how to write a program like this. Someday you might work on a project with me without knowing how to write a program like this. Then I would have to do you serious bodily harm. - Jack Klein

  6. #6
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    That's the conclusion I'm drawing also. Thanks for your help!
    If you understand what you're doing, you're not learning anything.

  7. #7
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    Quote Originally Posted by pianorain
    After a bit of modification, it's simple to check their output and see that it's the incorrect answer.

    As you can see, itsme86, your program generates the correct answer. The sample output on the site is incorrect.
    That's real teamwork!.

    I "reverse-engineered" the first flight results to deduce one possibility for an algorithm adjustment. I noticed that my answer for flight 2 was demonstrably better than the published result, but didn't try to figure out what happened there.

    Then pianorain "reverse-engineered" the results for flight 2 to make an adjustment in the input data.

    As I learned in a lab that I took about a thousand years ago: "If you know the right answer, you can get the right answer."

    Back in those days the phrase "reverse-engineering" was not in my lexicon; we called it "dry-labbing".

    (By the way --- since the creator of the problem also created the posted solution, I have to wonder: is there another way to intrepret the problem statement to come up with the posted solution with the given input data? Maybe someone should ask...)

    Regards,

    Dave
    Last edited by Dave Evans; 02-01-2005 at 09:08 AM.

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