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Math

  • Understanding math
  • Solved problems are presented in alphabetical order
Palindrome Number

↗ See LeetCode Problem #9​

public class Solution {    static boolean isPalindrome(int x) {        if (x < 0) {            return false;        }        int tempX = x;        int reversedX = 0;        while (tempX > 0) {            int remainderTempX = tempX % 10;            reversedX = reversedX * 10 + remainderTempX;            tempX = tempX / 10;        }        if (reversedX == x) {            return true;        } else {            return false;        }    }    public static void main(String[] args) {        // Example 1:        int x1 = 121;        //  O/P: true        // Example 2:        int x2 = -121;        //  O/P: false        // Example 3:        int x3 = 10;        //  O/P: false        System.out.println(isPalindrome(x1));        System.out.println(isPalindrome(x2));        System.out.println(isPalindrome(x3));    }}
Reverse Integer

↗ See LeetCode Problem #7​

public class Solution {    static int reverse(int x) {        //  Initialize the reversed integer to be built        int reversedInt = 0;        //  Check until given integer x is not 0,        //      since x is divided by 10 in every step        while (x != 0) {            //  Find the remainder to pop the last digit            int remainder = x % 10;            //  Divide by 10 to get rid of the last digit            x /= 10;            //  Check overflow condition on the positive side            if (reversedInt > Integer.MAX_VALUE / 10 ||                    (reversedInt == Integer.MAX_VALUE / 10 &&                            remainder > 7)) {                return 0;            }            //  Check overflow condition on the negative side            if (reversedInt < Integer.MIN_VALUE / 10 ||                    (reversedInt == Integer.MIN_VALUE / 10 &&                            remainder < -8)) {                return 0;            }            //  Build the reversed integer            reversedInt = reversedInt * 10 + remainder;        }        return reversedInt;    }    public static void main(String[] args) {        // Example 1:        int x1 = 123;        //  O/P: 321        // Example 2:        int x2 = -123;        //  O/P: -321        // Example 3:        int x3 = 120;        //  O/P: 21        System.out.println(reverse(x1));        System.out.println(reverse(x2));        System.out.println(reverse(x3));    }}
Roman to Integer

↗ See LeetCode Problem #13​

import java.util.HashMap;import java.util.Map;public class Solution {    static int romanToInt(String s) {        Map<String, Integer> valuesMap = new HashMap<>();        valuesMap.put("M", 1000);        valuesMap.put("D", 500);        valuesMap.put("C", 100);        valuesMap.put("L", 50);        valuesMap.put("X", 10);        valuesMap.put("V", 5);        valuesMap.put("I", 1);        int index = 0;        int totalSum = 0;        while (index < s.length()) {            String currentSymbol = s.substring(index, index +1);            int currentValue = valuesMap.get(currentSymbol);            int nextValue = 0;            if (index < s.length() - 1) {                String nextSymbol = s.substring(index + 1, index + 2);                nextValue = valuesMap.get(nextSymbol);            }            if (currentValue < nextValue) {                totalSum += (nextValue - currentValue);                index += 2;            } else {                totalSum += currentValue;                index += 1;            }        }       return totalSum;    }    public static void main(String[] args) {        // Example 1:        String s1 = "III";        //  O/P: 3        // Example 2:        String s2 = "LVIII";        //  O/P: 58        // Example 3:        String s3 = "MCMXCIV";        //  O/P: 1994        System.out.println(romanToInt(s1));        System.out.println(romanToInt(s2));        System.out.println(romanToInt(s3));    }}
Squares of a Sorted Array

↗ See LeetCode Problem #977​

import java.util.Arrays;public class Solution {    public static int[] sortedSquares(int[] nums) {        int leftIndex = 0;        int rightIndex = nums.length - 1;        int[] squaredArray = new int[nums.length];        for (int i = nums.length - 1; i >= 0; i--) {            if (Math.abs(nums[leftIndex]) < Math.abs(nums[rightIndex])) {                squaredArray[i] = nums[rightIndex] * nums[rightIndex];                rightIndex--;            } else {               squaredArray[i] = nums[leftIndex] * nums[leftIndex];               leftIndex++;            }        }        return squaredArray;    }    public static void main(String[] args) {        // Example 1:        int[] nums1 = {-4,-1,0,3,10};        //  O/P: [0,1,9,16,100]        // Example 2:        int[] nums2 = {-7,-3,2,3,11};        //  O/P: [4,9,9,49,121]        System.out.println(Arrays.toString(sortedSquares(nums1)));        System.out.println(Arrays.toString(sortedSquares(nums2)));    }}