feat: Implement solution for "How Many Numbers Are Smaller Than the C…

…urrent Number" problem

easy/how-many-numbers-are-smaller-than-the-current-number.test.ts

@@ -0,0 +1,34 @@
+// Problem: https://leetcode.com/problems/how-many-numbers-are-smaller-than-the-current-number/
+// Doc: https://leetcode.com/problems/how-many-numbers-are-smaller-than-the-current-number/solutions/5503382/efficient-count-of-smaller-numbers-than-current/
+const smallerNumbersThanCurrent = (nums: number[]): number[] => {
+  const counterMap: Record<number, number> = {};
+  const sortedNums = [...nums].sort((a, b) => a - b);
+  for (let i = 0; i < sortedNums.length; i++) {
+    const num = sortedNums[i];
+    if (!(num in counterMap)) counterMap[num] = i;
+  }
+
+  return nums.map((num) => counterMap[num]);
+};
+
+describe('How Many Numbers Are Smaller Than the Current Number', () => {
+  it('#1 should return [4, 0, 1, 1, 3]', () => {
+    const nums = [8, 1, 2, 2, 3];
+    expect(smallerNumbersThanCurrent(nums)).toStrictEqual([4, 0, 1, 1, 3]);
+  });
+
+  it('#2 should return [2, 1, 0, 3]', () => {
+    const nums = [6, 5, 4, 8];
+    expect(smallerNumbersThanCurrent(nums)).toStrictEqual([2, 1, 0, 3]);
+  });
+
+  it('#3 should return [0, 0, 0, 0]', () => {
+    const nums = [7, 7, 7, 7];
+    expect(smallerNumbersThanCurrent(nums)).toStrictEqual([0, 0, 0, 0]);
+  });
+
+  it('#4 should return [0, 0, 0, 0, 0]', () => {
+    const nums = [1, 1, 1, 1, 1];
+    expect(smallerNumbersThanCurrent(nums)).toStrictEqual([0, 0, 0, 0, 0]);
+  });
+});