3. 无重复字符的最长子串
题目链接：3. 无重复字符的最长子串 - 力扣（LeetCode）
题目难度：中等
代码：
class Solution {public int lengthOfLongestSubstring(String s) {Set<Character> set=new HashSet<>();int n=s.length();int r=-1,res=0;for(int i=0;i<n;i++){if(i!=0)set.remove(s.charAt(i-1));while(r+1<n&&!set.contains(s.charAt(r+1)))set.add(s.charAt(++r));res=Math.max(res,r-i+1);}return res;}
}12. 整数转罗马数字
题目链接：12. 整数转罗马数字 - 力扣（LeetCode）
题目难度：中等
代码：
class Solution {String[] thousands = {"", "M", "MM", "MMM"};String[] hundreds = {"", "C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM"};String[] tens = {"", "X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC"};String[] ones = {"", "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX"};public String intToRoman(int num) {StringBuffer roman = new StringBuffer();roman.append(thousands[num / 1000]);roman.append(hundreds[num % 1000 / 100]);roman.append(tens[num % 100 / 10]);roman.append(ones[num % 10]);return roman.toString();}
}49. 字母异位词分组
题目链接：49. 字母异位词分组 - 力扣（LeetCode）
题目难度：中等
代码：
class Solution {public List<List<String>> groupAnagrams(String[] strs) {Map<String,List<String>> map=new HashMap<>();for(String str:strs){int[] counts=new int[26];int length=str.length();for(int i=0;i<length;i++){counts[str.charAt(i)-'a']++;}StringBuffer sb=new StringBuffer();for(int i=0;i<26;i++){if(counts[i]!=0){sb.append((char)('a'+i));sb.append(counts[i]);}}String key=sb.toString();List<String> list=map.getOrDefault(key,new ArrayList<String>());list.add(str);map.put(key,list);}return new ArrayList<List<String>>(map.values());}
}73. 矩阵置零
题目链接：73. 矩阵置零 - 力扣（LeetCode）
题目难度：中等
代码：
class Solution {public void setZeroes(int[][] matrix) {int m = matrix.length, n = matrix[0].length;boolean flagCol0 = false;for (int i = 0; i < m; i++) {if (matrix[i][0] == 0) {flagCol0 = true;}for (int j = 1; j < n; j++) {if (matrix[i][j] == 0) {matrix[i][0] = matrix[0][j] = 0;}}}for (int i = m - 1; i >= 0; i--) {for (int j = 1; j < n; j++) {if (matrix[i][0] == 0 || matrix[0][j] == 0) {matrix[i][j] = 0;}}if (flagCol0) {matrix[i][0] = 0;}}}
}
