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[Interview]  URLify: -------------------------------------------------------------------------------------------------------------------------- Question: URLify: Write a method to replace all spaces in a string with ‘%20’, you may assume that the string has sufficient space at the end to hold the additional characters. Example  input: ' mr john smith '  output: ' mr %20john%20smith' --------------------------------------------------------------------------------------------------------------------------   Idea 1:  Start from the back and start replacing until the character is not ' ', and replace the characters in reverse order. Solution 1： public class Solution{ public String replace(char[] str) { boolean flag = false; StringBuffer sb = new StringBuffer(); for (int i = str.length - 1; i >= 0; i--) { if (str[i] != ' ') flag = true; if (flag == true) { if (str[i] == ' ') { s

[Interview] Check Permutation -------------------------------------------------------------------------------------------------------------------------- Question: Given 2 Strings, write a method to decide if one is a permutation of the other. -------------------------------------------------------------------------------------------------------------------------- Idea 1:  count the number of each character in first string and check if the number of each character in the 2nd string is the same as the 1st string. Solution 1： public class Solution{ boolean checker(String str1, String str2) { if (str1.length() != str2.length()) return false; int[] helper = new int[256]; for(int i = 0 ; i<str1.length();i++) { int index = str1.charAt(i); helper[index]++; } for(int i = 0 ; i<str2.length();i++) { int index = str2.charAt(i); helper[index]--; if(helper[index]<0) return false; } return true; } } ---------------------

[Interview] Reverse C/C++ Style String  Question: Write code to reverse a C-Style String. (C-String means that “abcd” is represented as five characters, including the null character.) Solution： public class Solution{ public String reverse(String str) { int p1 = 0; int p2 = str.length() - 1; char temp; char[] c = new char[p2]; c = str.toCharArray(); while (p1 < p2) { temp = c[p1]; c[p1] = c[p2]; c[p2] = temp; p1++; p2--; } return new String(c); } } Complexity Analysis: Time Complexity: \(O(n)\) Space Complexity: \(O(n)\)

[Interview] Check if String has Unique Characters Implement an algorithm to determine if a string has all unique characters What if you can not use additional data structure? package com.Array_Strings; /** * @Question: 1-1. Implement an algorithm to determine if a string has all * unique characters What if you can not use additional data * structure? */ public class Ans1_1 { public boolean helper(String str) { boolean[] map = new boolean[256]; for (int i = 0; i < str.length(); i++) { int val = str.charAt(i); if (map[val]) return false; map[val] = true; } return true; } } Complexity Analysis: Time Complexity: \(O(n)\) Space Complexity: \(O(n)\) Here is my Video Explanation