Merge pull request #91 from Joshua-Lu/patch-7

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

@@ -212,79 +212,76 @@ public:
 
 
 Java：
-```java
+
+```Java
 class Solution {
-  public String reverseWords(String s) {
-		char[] chars = s.toCharArray();
-		// 1.双指针去除空格
-		// 去除头尾空格
-		int head = 0;
-		while (chars[head] == ' ') {
-			head ++;
-		}
-		int tail = chars.length - 1;
-		while (chars[tail] == ' ') {
-			tail --;
-		}
+   /**
+     * 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();
+    }
 
-		// 去除中间空格
-		int p1 = head;
-		int p2 = head + 1;
-		while (p2 <= tail) {
-			if (chars[p2 -1] == ' ' && chars[p2] == ' ') {
-				p2 ++;
-				continue;
-			}
-			chars[p1 + 1] = chars[p2];
-			p1 ++;
-			p2 ++;
-		}
+    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;
+    }
 
-		tail = p1;
+    /**
+     * 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 + "]");
+    }
 
-		// 2.双指针翻转整个字符串
-		chars = reverse(chars, head, tail);
-
-		// 3.双指针翻转每个单词
-		p1 = head;
-		p2 = head;
-
-		for (int i = head; i <= tail;) {
-			int add = 0;
-			while (i + add <= tail && chars[i + add] != ' ') {
-				add ++;
-			}
-
-			if (i + add != tail) {
-				reverse(chars, i, i + add - 1);
-				i += add + 1;
-			} else {
-				reverse(chars, i, tail);
-				i = tail + 1;
-			}
-		}
-
-		return new String(chars, head, tail - head + 1);
-  }
-
-  char[] reverse(char[] chars, int begin, int end) {
-		int p1 = begin;
-		int p2 = end;
-
-		while (p1 < p2) {
-			chars[p1] ^= chars[p2];
-			chars[p2] ^= chars[p1];
-			chars[p1] ^= chars[p2];
-
-			p1 ++;
-			p2 --;
-		}
-		return chars;
-	}
+    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：