added challenge 15

Author: mathisve

.gitignore

@@ -1 +1,2 @@
 10-gaussianCurve/kek.zip
+.idea/

015-hexToDecimal/README.md

@@ -0,0 +1,24 @@
+Welcome @Challengers to the 15th #code4bytes challenge!
+
+The first challenge of 2021!
+Happy New Year, Merry Christmas, yada yada.
+Sorry for the immensely long delay but I've been very with a bunch of stuff. You know how it is.
+
+Today's challenge is about converting hexadecimals to integers.
+In the file `tests.json` you find a bunch of test cases that you will need to write a function for.
+I think it's pretty self-explanatory. `input` is the one and only parameter of the function (also a string), `result` is the expected result (integer) and `fails` is if whether the function should return an error in case there is an invalid character in the input (represented by a boolean, true for should return an error. In the case of an error the result is 0).
+
+Write a function that converts a string representing a hexadecimal number to a decimal integer.
+Run through all the examples, and print each one out (or throw an error if there is a mismatch. Make it extra visibile so I don't have to spend 3 hours checking all the results thanks haha)
+
+No external libraries can be used to do the converting for you (or if your language happens to have a function that does it for you), no points will be rewarded if you do! What is allowed is libraries that convert strings to integers, maths functions, logging, etc. Also try not to inmediately google how to convert hex to decimal, otherwise where is the fun in coming up with your own algorithm. Direct copying of code is also forbidden per the rules (and a ban-able offence might I add.)
+
+All reasonable languages are allowed (no brainfuck, assembly, etc).
+Submit your results and source code to me to receive your points!
+
+- 1st place: 300.000 bytes!
+- 2nd place: 200.000 bytes!
+- 3rd place: 150.000 bytes!
+- Runner up: 75.000 bytes!
+
+Good luck, have fun and don't cheat!

015-hexToDecimal/base_solution.go

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+package main
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"math"
+	"strconv"
+	"strings"
+)
+
+type Test struct {
+	Input  string `json:"input"`
+	Result int    `json:"result"`
+	Fails  bool   `json:"fails"`
+}
+
+var hexMap = map[string]int{
+	"A": 10,
+	"B": 11,
+	"C": 12,
+	"D": 13,
+	"E": 14,
+	"F": 15,
+}
+
+func hexToDecimal(hex string) (decimal int, err error) {
+	split := strings.Split(hex, "")
+	length := len(split)
+
+	for i, char := range split {
+		var num int
+		num, strConvErr := strconv.Atoi(char)
+		if strConvErr != nil {
+			if num = hexMap[char]; num == 0 {
+				return 0, errors.New(fmt.Sprintf("hex: %v not valid", hex))
+			}
+		}
+
+		decimal += num * int(math.Pow(16, float64(length-i+-1)))
+	}
+
+	return decimal, nil
+}
+
+func readFile(filename string) []byte {
+	b, err := ioutil.ReadFile(filename)
+	if err != nil {
+		log.Println(err)
+	}
+
+	return b
+}
+
+func main() {
+
+	var tests []Test
+
+	b := readFile("tests.json")
+	err := json.Unmarshal(b, &tests)
+	if err != nil {
+		fmt.Println(err)
+	}
+
+	for _, test := range tests {
+		r, err := hexToDecimal(test.Input)
+
+		if err != nil && test.Fails == true {
+			fmt.Printf("Testcase: '%v' | Expected: err, got: err\n", test.Input)
+		} else {
+			fmt.Printf("Testcase: '%v' | Expected: %v, got: %v\n", test.Input, test.Result, r)
+		}
+
+	}
+}

015-hexToDecimal/main_test.go

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+package main
+
+import (
+	"encoding/json"
+	"log"
+	"os"
+	"testing"
+)
+
+func TestHexToDecimal(T *testing.T) {
+
+	var tests []Test
+
+	f, err := os.Open("tests.json")
+	if err != nil {
+		log.Println(err)
+	}
+
+	var b []byte
+	_, err = f.Read(b)
+	if err != nil {
+		log.Println(err)
+	}
+
+	err = json.Unmarshal(b, &tests)
+
+	for _, test := range tests {
+		r, err := hexToDecimal(test.Input)
+		if err != nil && test.Fails == true {
+			continue
+		}
+
+		if err != nil {
+			T.Fatalf(`Testcase: "%v" failed with error: %v`, test.Input, err)
+		}
+
+		if r != test.Result {
+			T.Fatalf(`Testcase: "%v" failed. Expected: %v, got: %v`, test.Input, test.Result, r)
+		}
+	}
+}

015-hexToDecimal/tests.json

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+[
+  {
+    "input":"0",
+    "result":0,
+    "fails":false
+  },
+  {
+    "input":"01",
+    "result":1,
+    "fails":false
+  },
+  {
+    "input":"1",
+    "result":1,
+    "fails":false
+  },
+  {
+    "input":"9",
+    "result":9,
+    "fails":false
+  },
+  {
+    "input":"11",
+    "result":17,
+    "fails":false
+  },
+  {
+    "input":"99",
+    "result":153,
+    "fails":false
+  },
+  {
+    "input":"FFF",
+    "result":4095,
+    "fails":false
+  },
+  {
+    "input":"383AFB",
+    "result":3685115,
+    "fails":false
+  },
+  {
+    "input":"AA",
+    "result":170,
+    "fails":false
+  },
+  {
+    "input":"12346789ABCDEF",
+    "result":5124168876805615,
+    "fails":false
+  },
+  {
+    "input":"FEDCBA987654321",
+    "result":1147797409030816545,
+    "fails":false
+  },
+  {
+    "input":"ABCDEFG012345789",
+    "result":0,
+    "fails":true
+  },
+  {
+    "input":"&##$})!}@!{}",
+    "result":0,
+    "fails":true
+  },
+  {
+    "input":"1 2",
+    "result":0,
+    "fails":true
+  }
+]