Lexographically smallest after a swap (#99)

Author: ignacio-chiazzo

LeetcodeProblems/Algorithms/easy/Lexographic_smallest_after_swap.js

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+/*
+3216. Lexicographically Smallest String After a Swap
+https://leetcode.com/problems/lexicographically-smallest-string-after-a-swap/description/
+
+Problem:
+Given a string s containing only digits, return the lexicographically smallest string
+that can be obtained after swapping adjacent digits in s with the same parity at most once.
+
+Digits have the same parity if both are odd or both are even. For example, 5 and 9, as well as 2 and 4,
+have the same parity, while 6 and 9 do not.
+
+Example 1:
+
+Input: s = "45320"
+
+Output: "43520"
+
+Explanation:
+
+s[1] == '5' and s[2] == '3' both have the same parity, and swapping them results in the lexicographically smallest string.
+
+Example 2:
+
+Input: s = "001"
+
+Output: "001"
+
+Explanation:
+
+There is no need to perform a swap because s is already the lexicographically smallest.
+
+
+Constraints:
+
+2 <= s.length <= 100
+s consists only of digits.
+*/
+
+/*
+Approach:
+
+Checking if the present digit is greater than the next digit, if yes then checking the parity of the digit.
+if both have the same parity swap the number. since this operation can be done at max once, break the loop after the first swap.
+return the updated number
+
+What is parity of a number?
+Parity: the property of an integer of whether it is even or odd
+
+how to check the parity of the number:
+- using the & operation on the last bit,
+- if (last bit)&1 == 1, means the last bit was 1. means Odd (ex: 3 has a bit representation of 11)
+- if (last bit)&1 == 0, means last bit was 0. means Even number ( ex: 2 has a bit representation of 10)
+
+*/
+
+
+/**
+ * @param {string} s
+ * @return {string}
+ */
+var getSmallestString = function(s) {
+  let arr = s.split("").map(Number);
+
+  const getParity = (num) => {
+    if(num&1 === 0) return "even";
+    else return "odd";
+  };
+
+  for(let i = 0; i< s.length - 1; i++) {
+    if(arr[i] > arr[i+1] && getParity(arr[i]) === getParity(arr[i + 1])) {
+      let tmp = arr[i+1];
+      arr[i+1] = arr[i];
+      arr[i] = tmp;
+      break;
+    }
+  }
+
+  return arr.join("");
+};
+
+module.exports.getSmallestString = getSmallestString;

LeetcodeProblemsTests/Algorithms/easy/Lexographic_smallest_after_swap.js

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+const assert = require("assert");
+const bitReverseToMakeNumberEqual = require("../../../LeetcodeProblems/Algorithms/easy/Lexographic_smallest_after_swap").getSmallestString;
+
+
+function test() {
+  assert.deepEqual(
+    getSmallestString("45320"),
+    "43520"
+  );
+  assert.deepEqual(
+    getSmallestString("001"),
+    "001"
+  );
+);
+}
+
+module.exports.test = test;