feat: update lcof solutions

Author: yanglbme

lcof/面试题03. 数组中重复的数字/README.md

@@ -47,11 +47,9 @@ class Solution:
 ```java
 class Solution {
     public int findRepeatNumber(int[] nums) {
-        for (int i = 0, len = nums.length; i < len; ++i) {
-            while (i != nums[i]) {
-                if (nums[i] == nums[nums[i]]) {
-                    return nums[i];
-                }
+        for (int i = 0, n = nums.length; i < n; ++i) {
+            while (nums[i] != i) {
+                if (nums[i] == nums[nums[i]]) return nums[i];
                 swap(nums, i, nums[i]);
             }
         }

lcof/面试题03. 数组中重复的数字/Solution.java

@@ -1,10 +1,8 @@
 class Solution {
     public int findRepeatNumber(int[] nums) {
-        for (int i = 0, len = nums.length; i < len; ++i) {
-            while (i != nums[i]) {
-                if (nums[i] == nums[nums[i]]) {
-                    return nums[i];
-                }
+        for (int i = 0, n = nums.length; i < n; ++i) {
+            while (nums[i] != i) {
+                if (nums[i] == nums[nums[i]]) return nums[i];
                 swap(nums, i, nums[i]);
             }
         }

lcof/面试题04. 二维数组中的查找/README.md

@@ -59,20 +59,13 @@ class Solution:
 ```java
 class Solution {
     public boolean findNumberIn2DArray(int[][] matrix, int target) {
-        if (matrix == null || matrix.length == 0 || matrix[0] == null || matrix[0].length == 0) {
-            return false;
-        }
-        int rows = matrix.length, cols = matrix[0].length;
-        int i = rows - 1, j = 0;
-        while (i >= 0 && j < cols) {
-            if (matrix[i][j] == target) {
-                return true;
-            }
-            if (matrix[i][j] > target) {
-                --i;
-            } else {
-                ++j;
-            }
+        int m, n;
+        if (matrix == null || (m = matrix.length) == 0 || matrix[0] == null || (n = matrix[0].length) == 0) return false;
+        int i = 0, j = n - 1;
+        while (i < m && j >= 0) {
+            if (matrix[i][j] == target) return true;
+            if (matrix[i][j] > target) --j;
+            else ++i;
         }
         return false;
     }

lcof/面试题04. 二维数组中的查找/Solution.java

@@ -1,19 +1,12 @@
 class Solution {
     public boolean findNumberIn2DArray(int[][] matrix, int target) {
-        if (matrix == null || matrix.length == 0 || matrix[0] == null || matrix[0].length == 0) {
-            return false;
-        }
-        int rows = matrix.length, cols = matrix[0].length;
-        int i = rows - 1, j = 0;
-        while (i >= 0 && j < cols) {
-            if (matrix[i][j] == target) {
-                return true;
-            }
-            if (matrix[i][j] > target) {
-                --i;
-            } else {
-                ++j;
-            }
+        int m, n;
+        if (matrix == null || (m = matrix.length) == 0 || matrix[0] == null || (n = matrix[0].length) == 0) return false;
+        int i = 0, j = n - 1;
+        while (i < m && j >= 0) {
+            if (matrix[i][j] == target) return true;
+            if (matrix[i][j] > target) --j;
+            else ++i;
         }
         return false;
     }

lcof/面试题05. 替换空格/README.md

@@ -31,6 +31,8 @@ class Solution:
 
 ### **Java**
 
+- 使用 replace：
+
 ```java
 class Solution {
     public String replaceSpace(String s) {
@@ -39,6 +41,21 @@ class Solution {
 }
 ```
 
+- 使用 StringBuilder：
+
+```java
+class Solution {
+    public String replaceSpace(String s) {
+        StringBuilder sb = new StringBuilder();
+        char[] chars = s.toCharArray();
+        for (char c : chars) {
+            sb.append(c == ' ' ? "%20" : c);
+        }
+        return sb.toString();
+    }
+}
+```
+
 ### **JavaScript**
 
 ```js

lcof/面试题06. 从尾到头打印链表/README.md

@@ -17,7 +17,7 @@
 
 ## 解法
 
-栈实现。
+栈实现。或者其它方式，见题解。
 
 <!-- tabs:start -->
 
@@ -41,6 +41,8 @@ class Solution:
 
 ### **Java**
 
+- 栈实现：
+
 ```java
 /**
  * Definition for singly-linked list.
@@ -67,6 +69,38 @@ class Solution {
 }
 ```
 
+- 先计算链表长度 n，然后创建一个长度为 n 的结果数组。最后遍历链表，依次将节点值存放在数组上（从后往前）。
+
+```java
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    public int[] reversePrint(ListNode head) {
+        if (head == null) return new int[]{};
+        // 计算链表长度n
+        int n = 0;
+        ListNode cur = head;
+        while (cur != null) {
+            ++n;
+            cur = cur.next;
+        }
+        int[] res = new int[n];
+        cur = head;
+        while (cur != null) {
+            res[--n] = cur.val;
+            cur = cur.next;
+        }
+        return res;
+    }
+}
+```
+
 ### **Go**
 
 ```go

lcof/面试题06. 从尾到头打印链表/Solution.java

@@ -8,15 +8,19 @@
  */
 class Solution {
     public int[] reversePrint(ListNode head) {
-        Stack<Integer> s = new Stack<>();
-        while (head != null) {
-            s.push(head.val);
-            head = head.next;
+        if (head == null) return new int[]{};
+        // 计算链表长度n
+        int n = 0;
+        ListNode cur = head;
+        while (cur != null) {
+            ++n;
+            cur = cur.next;
         }
-        int[] res = new int[s.size()];
-        int i = 0;
-        while (!s.isEmpty()) {
-            res[i++] = s.pop();
+        int[] res = new int[n];
+        cur = head;
+        while (cur != null) {
+            res[--n] = cur.val;
+            cur = cur.next;
         }
         return res;
     }