Update 0151.翻转字符串里的单词.md

添加 0151.翻转字符串里的单词 Java版本

problems/0151.翻转字符串里的单词.md

@@ -212,7 +212,74 @@ public:
 
 
 Java：
+```Java
+class Solution {
+   /**
+     * 不使用Java内置方法实现
+     * <p>
+     * 1.去除首尾以及中间多余空格
+     * 2.反转整个字符串
+     * 3.反转各个单词
+     */
+    public String reverseWords(String s) {
+        // System.out.println("ReverseWords.reverseWords2() called with: s = [" + s + "]");
+        // 1.去除首尾以及中间多余空格
+        StringBuilder sb = removeSpace(s);
+        // 2.反转整个字符串
+        reverseString(sb, 0, sb.length() - 1);
+        // 3.反转各个单词
+        reverseEachWord(sb);
+        return sb.toString();
+    }
 
+    private StringBuilder removeSpace(String s) {
+        // System.out.println("ReverseWords.removeSpace() called with: s = [" + s + "]");
+        int start = 0;
+        int end = s.length() - 1;
+        while (s.charAt(start) == ' ') start++;
+        while (s.charAt(end) == ' ') end--;
+        StringBuilder sb = new StringBuilder();
+        while (start <= end) {
+            char c = s.charAt(start);
+            if (c != ' ' || sb.charAt(sb.length() - 1) != ' ') {
+                sb.append(c);
+            }
+            start++;
+        }
+        // System.out.println("ReverseWords.removeSpace returned: sb = [" + sb + "]");
+        return sb;
+    }
+
+    /**
+     * 反转字符串指定区间[start, end]的字符
+     */
+    public void reverseString(StringBuilder sb, int start, int end) {
+        // System.out.println("ReverseWords.reverseString() called with: sb = [" + sb + "], start = [" + start + "], end = [" + end + "]");
+        while (start < end) {
+            char temp = sb.charAt(start);
+            sb.setCharAt(start, sb.charAt(end));
+            sb.setCharAt(end, temp);
+            start++;
+            end--;
+        }
+        // System.out.println("ReverseWords.reverseString returned: sb = [" + sb + "]");
+    }
+
+    private void reverseEachWord(StringBuilder sb) {
+        int start = 0;
+        int end = 1;
+        int n = sb.length();
+        while (start < n) {
+            while (end < n && sb.charAt(end) != ' ') {
+                end++;
+            }
+            reverseString(sb, start, end - 1);
+            start = end + 1;
+            end = start + 1;
+        }
+    }
+}
+```
 
 Python：