feat: add range extraction solution

Author: marcode24

codewars/range-extraction/README.md

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+# Range Extraction
+
+## Description
+
+A format for expressing an ordered list of integers is to use a comma separated list of either
+
+- individual integers
+- or a range of integers denoted by the starting integer separated from the end integer in the range by a dash, '-'. The range includes all integers in the interval including both endpoints. It is not considered a range unless it spans at least 3 numbers. For example "12,13,15-17"
+
+Complete the solution so that it takes a list of integers in increasing order and returns a correctly formatted string in the range format.
+
+Example:
+
+```js
+solution([
+  -10, -9, -8, -6, -3, -2, -1, 0, 1, 3, 4, 5, 7, 8, 9, 10, 11, 14, 15, 17, 18,
+  19, 20,
+]);
+// returns "-10--8,-6,-3-1,3-5,7-11,14,15,17-20"
+```

codewars/range-extraction/solution.js

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+const solution = (list) => {
+  let result = '';
+  let start = list[0];
+  let end = list[0];
+  let i = 1;
+
+  while (i < list.length) {
+    if (list[i] - list[i - 1] === 1) {
+      end = list[i];
+    } else {
+      if (start === end) {
+        result += `${start},`;
+      } else if (end - start === 1) {
+        result += `${start},${end},`;
+      } else {
+        result += `${start}-${end},`;
+      }
+      start = list[i];
+      end = list[i];
+    }
+    i += 1;
+  }
+  if (start === end) {
+    result += `${start}`;
+  } else if (end - start === 1) {
+    result += `${start},${end}`;
+  } else {
+    result += `${start}-${end}`;
+  }
+
+  return result;
+};
+
+module.exports = solution;

codewars/range-extraction/solution.test.js

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+const solution = require('./solution');
+
+describe('Range extraction', () => {
+  const testCases = [
+    {
+      input: [-6, -3, -2, -1, 0, 1, 3, 4, 5, 7, 8, 9, 10, 11, 14, 15, 17, 18, 19, 20],
+      output: '-6,-3-1,3-5,7-11,14,15,17-20',
+    },
+    {
+      input: [-3, -2, -1, 2, 10, 15, 16, 18, 19, 20],
+      output: '-3--1,2,10,15,16,18-20',
+    },
+    {
+      input: [-10, -9, -8, -6, -3, -2, -1, 0, 1, 3, 4, 5, 7, 8, 9, 10, 11, 14, 15, 17,
+        18, 19, 20],
+      output: '-10--8,-6,-3-1,3-5,7-11,14,15,17-20',
+    },
+    {
+      input: [-3, -2, -1, 2, 10, 15, 16, 18, 19, 20, 22, 23],
+      output: '-3--1,2,10,15,16,18-20,22,23',
+    },
+  ];
+
+  it('should return a string', () => {
+    expect(typeof solution([-1, 0, 1, 2, 6, 7, 9])).toBe('string');
+  });
+
+  it.each(testCases)('should return the correct output', (testCase) => {
+    expect(solution(testCase.input)).toBe(testCase.output);
+  });
+});