401. Binary Watch

Author: antisilent

solutions/401-binary-watch/README.md

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+# [401. Binary Watch](https://leetcode.com/problems/binary-watch/description/) [🟢](## "Easy")
+
+## Description:
+
+A binary watch has 4 LEDs on the top to represent the hours (0-11), and 6 LEDs on the bottom to represent the minutes (0-59). Each LED represents a zero or one, with the least significant bit on the right.
+
+For example, the below binary watch reads `4:51`.
+
+    0 1 0 0
+    1 1 0 0 1 1
+
+Given an integer `turnedOn` which represents the number of LEDs that are currently on, return all possible times the watch could represent. You may return the answer in any order.
+
+The hour must not contain a leading zero.
+
+* For example, `"01:00"` is not valid. It should be `"1:00"`.
+
+The minute must consist of two digits and may contain a leading zero.
+
+* For example, `"10:2"` is not valid. It should be `"10:02"`.
+
+
+Example 1:
+
+    Input: turnedOn = 1
+    Output: ["0:01","0:02","0:04","0:08","0:16","0:32","1:00","2:00","4:00","8:00"]
+
+Example 2:
+
+    Input: turnedOn = 9
+    Output: []
+
+
+Constraints:
+
+0 <= turnedOn <= 10

solutions/401-binary-watch/solution.js

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+/**
+ * @param {number} turnedOn
+ * @return {string[]}
+ */
+export default function readBinaryWatch(turnedOn) {
+  // if (turnedOn === 0) return ['0:00'];
+  // if (turnedOn > 8) return [];
+  const countBits = (dec) => dec.toString(2).split('').reduce((a, b) => a + parseInt(b), 0);
+  const results = [];
+
+  for (let h = 0; h < 12; h++) {
+
+    const hbits = countBits(h);
+    for (let m = 0; m < 60; m++) {
+      const mbits = countBits(m);
+      if (hbits + mbits === turnedOn) {
+        results.push(`${h}:${m.toString().padStart(2, '0')}`);
+      }
+    }
+  }
+
+  return results;
+};
+
+// TODO: Why is this a better solution?
+// /**
+//  * @param {number} turnedOn
+//  * @return {string[]}
+//  */
+// export default function readBinaryWatch(turnedOn) {
+//   let res = [];
+//   let count = (n) => n ? (n % 2) + count(n >> 1) : 0;
+//   for (let h = 0; h < 12; h++) {
+//     for (let m = 0; m < 60; m++) {
+//       if (count(h) + count(m) == turnedOn) {
+//         res.push(`${h}:${m  < 10 ? '0' + m : m}`);
+//       }
+//     }
+//   }
+//   return res;
+// };

solutions/401-binary-watch/solution.test.js

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+import solution from './solution';
+
+describe('401. Binary Watch', () => {
+  Object.entries({
+    0: ['0:00'],
+    1: ['0:01','0:02','0:04','0:08','0:16','0:32','1:00','2:00','4:00','8:00'],
+    8: ['7:31','7:47','7:55','7:59','11:31','11:47','11:55','11:59'],
+    // 9: [],
+  }).forEach(([input, expected], i) => {
+    it(`Case ${i} (input = ${input})`, () => {
+      expect(solution(parseInt(input))).toStrictEqual(expected);
+    });
+  })
+});