一、字符串反轉
把一個句子中的打次進行反轉，比如“how are you” ,變為 “you are how”
// 字符串反轉 public class StringTest { // 字符反轉的方法 private void swap(char[] c, int front, int end) { if (front > end || end >= c.length) { return; } while (front < end) { char tmp = c[front]; c[front] = c[end]; c[end] = tmp; front++; end--; } } // O(n) public String swapStr(String str) { char[] cArr = str.toCharArray(); // 整個字符串的字符反轉 swap(cArr, 0, cArr.length - 1); // 反轉整個字符串中的所有字母，how are you -> uoy era woh int begin = 0; // 對字符串中的每個單詞反轉，除了最后一單詞 for (int i = 0; i < cArr.length; i++) { if (cArr[i] == ' ') { swap(cArr, begin, i - 1); begin = i + 1; } } // 最后一個單詞的反轉 swap(cArr, begin, cArr.length - 1); return new String(cArr); } public static void main(String[] args) { String str = "how are you"; System.out.println(new StringTest().swapStr(str)); } }
二、判斷字符串是否由相同的字符組成
判斷連個字符串的字母個字母的個數是否一樣，順序可以不同， 如“aaaabc” 和“cbaaaa”是相同的
// 判斷字符串是否由相同的字符組成 public class StringTest { // 方法一 可以死任意字符 O(nlogn) public boolean compareStr(String str1, String str2) { byte[] bs1 = str1.getBytes(); byte[] bs2 = str2.getBytes(); Arrays.sort(bs1); Arrays.sort(bs2); str1 = new String(bs1); str2 = new String(bs2); if (str1.equals(str2)) { return true; } else { return false; } } // 只能是ASCII碼 方法二 O(n) public boolean compareStr2(String str1, String str2) { byte[] bs1 = str1.getBytes(); byte[] bs2 = str2.getBytes(); int bCount[] = new int[256]; for (int i = 0; i < bs1.length; i++) bCount[bs1[i] ]++; for (int i = 0; i < bs2.length; i++) bCount[bs2[i] ]--; for (int i = 0; i < 256; i++) { if (bCount[i] != 0) { return false; } } return true; } public static void main(String[] args) { String str1 = "aaaabbc"; String str2 = "cbaaaab"; System.out.println(new StringTest().compareStr2(str1, str2)); } }
三、字符串中單詞的統計
給定一段空格分開的字符串，判斷單詞的個數
// 字符串中單詞的統計 public class StringTest { // O(n) public int wordCount(String str) { int word = 0; int count = 0; for (int i = 0; i < str.length(); i++) { if (str.charAt(i) == ' ') word = 0; else if (word == 0 ) { word = 1; count++; } } return count; } public static void main(String[] args) { String str = "i am a good boy"; System.out.println(new StringTest().wordCount(str)); } }
四、刪除字符串中重復的字符
刪除字符串中國重復的字符。如good -> god
// 刪除字符串中重復的字符 public class StringTest { // O(n^2) public String removeDuplicate(String str) { char[] cs = str.toCharArray(); int n = cs.length; for (int i = 0; i < n; i++) { if (cs[i] == '\0') continue; for (int j = i + 1; j < n; j++) { if (cs[j] == '\0') continue; if (cs[i] == cs[j]) cs[j] = '\0'; } } int be = 0; for (int i = 0; i < n; i++) { if (cs[i] != '\0') cs[be++] =cs[i]; } return new String(cs, 0, be); } // 方法二： O(n) public String removeDuplicate2(String str) { char[] cs = str.toCharArray(); int n = cs.length; int count[] = new int[256]; for (int i = 0; i < cs.length; i++) { if (count[cs[i]] != 0) cs[i] = '\0'; count[cs[i]]++; } int be = 0; for (int i = 0; i < n; i++) { if (cs[i] != '\0') cs[be++] = cs[i]; } return new String(cs, 0, be); } public static void main(String[] args) { String str = "aaaabbc"; System.out.println(new StringTest().removeDuplicate(str)); } }
五、按要求打印給定數組的排列情況
如1，2,2,3,4,5，要求第四位不為4,3和5不能相連
// 按要求打印數組的排列情況 import java.util.HashSet; import java.util.Iterator; import java.util.Set; public class StringTest { boolean visited[]; String combination = ""; int graph[][] = null; public void getAllCombination(int arr[]) { int n = arr.length; graph = new int[n][n]; visited = new boolean[n]; buildGraph(arr, graph); Set<String> set = new HashSet<>(); for (int i = 0; i < n; i++) { depthFirstSearch(i, set, arr); } Iterator<String> iterator = set.iterator(); while (iterator.hasNext()) { String string = (String) iterator.next(); System.out.println(string); } } /** * 按照深度優先遍歷 圖，將符合要求的組合加入到set中，自動去重 * * @param start * @param set * @param arr */ private void depthFirstSearch(int start, Set<String> set, int arr[]) { visited[start] = true; combination += arr[start]; if (combination.length() == arr.length) { if (combination.indexOf("4") != 2) { set.add(combination); } } for (int j = 0; j < arr.length; j++) { if (graph[start][j] == 1 && visited[j] == false) depthFirstSearch(j, set, arr); } // 什么意思? combination = combination.substring(0, combination.length() - 1); visited[start] = false; } /** * 根據傳入的數構建一個圖，圖中的 3,5 不能相連 * * @param arr * @param graph * @return */ private int[][] buildGraph(int arr[], int[][] graph) { for (int i = 0; i < arr.length; i++) { for (int j = 0; j < arr.length; j++) { if (arr[i] == arr[j]) graph[i][j] = 0; else graph[i][j] = 1; } } graph[3][5] = 0; graph[5][3] = 0; return graph; } public static void main(String[] args) { int arr[] = { 1, 2, 2, 3, 4, 5 }; new StringTest().getAllCombination(arr); } }
六、輸出字符串的所有組合
給定一個字符串，輸出該字符串中字符的所有組合
// 輸出字符串的所有組合 public class StringTest { public void combineRecursive(char[] c, int begin, int len, StringBuffer sb) { if (len == 0) { System.out.print(sb + " "); return; } if (begin == c.length) return; sb.append(c[begin]); combineRecursive(c, begin + 1, len - 1, sb); sb.deleteCharAt(sb.length() - 1); combineRecursive(c, begin + 1, len, sb); } public static void main(String[] args) { String s = "abc"; char[] cs = s.toCharArray(); StringBuffer sb = new StringBuffer(); for (int j = 1; j < cs.length; j++) { new StringTest().combineRecursive(cs, 0, j, sb); } } }