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Main.java

+import java.util.*;
 class Main {
   public static void main(String[] args) {
-    System.out.println("Hello world!");
+    Scanner scanner = new Scanner(System.in);
+    String str = scanner.nextLine();
+    char[] ch = str.toCharArray();
+    int len = ch.length;
+    //逆置整个字符串
+    reverse(ch,0,len-1);
+    //逆置每个单独的单词
+    int i = 0;
+    while (i < len){
+        int j = i;
+        while (j < len && ch[j] != ' '){
+            j++;
+        }
+        if (j < len){
+            reverse(ch,i ,j-1);
+            i = j + 1;
+        }else {
+            //此时逆置单词已经到了最后一个
+            reverse(ch, i, j-1);
+            i = j;
+        }
+    }
+    // 将字符数组准转换为字符串
+    String s = new String(ch);
+    System.out.println(s);
+  }
+  public static void reverse(char[] arr, int start, int end){
+    while (start <end){
+        char tmp = arr[start];
+        arr[start] = arr[end];
+        arr[end] = tmp;
+        start++;
+        end--;
+    }
   }
 }
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