diff --git a/problems/0046.全排列.md b/problems/0046.全排列.md
index df9394eb..001c249e 100644
--- a/problems/0046.全排列.md
+++ b/problems/0046.全排列.md
@@ -183,6 +183,32 @@ class Solution {
     }
 }
 ```
+```java
+// 解法2：通过判断path中是否存在数字，排除已经选择的数字
+class Solution {
+    List<List<Integer>> result = new ArrayList<>();
+    LinkedList<Integer> path = new LinkedList<>();
+    public List<List<Integer>> permute(int[] nums) {
+        if (nums.length == 0) return result;
+        backtrack(nums, path);
+        return result;
+    }
+    public void backtrack(int[] nums, LinkedList<Integer> path) {
+        if (path.size() == nums.length) {
+            result.add(new ArrayList<>(path));
+        }
+        for (int i =0; i < nums.length; i++) {
+            // 如果path中已有，则跳过
+            if (path.contains(nums[i])) {
+                continue;
+            } 
+            path.add(nums[i]);
+            backtrack(nums, path);
+            path.removeLast();
+        }
+    }
+}
+```
 
 Python：
 ```python3
diff --git a/problems/0056.合并区间.md b/problems/0056.合并区间.md
index 2322951a..82ca29e6 100644
--- a/problems/0056.合并区间.md
+++ b/problems/0056.合并区间.md
@@ -157,6 +157,28 @@ class Solution {
     }
 }
 ```
+```java
+// 版本2
+class Solution {
+    public int[][] merge(int[][] intervals) {
+        LinkedList<int[]> res = new LinkedList<>();
+        Arrays.sort(intervals, (o1, o2) -> Integer.compare(o1[0], o2[0]));
+        res.add(intervals[0]);
+        for (int i = 1; i < intervals.length; i++) {
+            if (intervals[i][0] <= res.getLast()[1]) {
+                int start = res.getLast()[0];
+                int end = Math.max(intervals[i][1], res.getLast()[1]);
+                res.removeLast();
+                res.add(new int[]{start, end});
+            }
+            else {
+                res.add(intervals[i]);
+            }         
+        }
+        return res.toArray(new int[res.size()][]);
+    }
+}
+```
 
 Python：
 ```python
diff --git a/problems/0134.加油站.md b/problems/0134.加油站.md
index ff3bc8b2..9aa88fce 100644
--- a/problems/0134.加油站.md
+++ b/problems/0134.加油站.md
@@ -200,6 +200,7 @@ public:
 
 Java：
 ```java
+// 解法1
 class Solution {
     public int canCompleteCircuit(int[] gas, int[] cost) {
         int sum = 0;
@@ -221,7 +222,26 @@ class Solution {
     }
 }
 ```
-
+```java
+// 解法2
+class Solution {
+    public int canCompleteCircuit(int[] gas, int[] cost) {
+        int curSum = 0;
+        int totalSum = 0;
+        int index = 0;
+        for (int i = 0; i < gas.length; i++) {
+            curSum += gas[i] - cost[i];
+            totalSum += gas[i] - cost[i];
+            if (curSum < 0) {
+                index = (i + 1) % gas.length ; 
+                curSum = 0;
+            }
+        }
+        if (totalSum < 0) return -1;
+        return index;
+    }
+}
+```
 Python：
 ```python
 class Solution:
diff --git a/problems/1005.K次取反后最大化的数组和.md b/problems/1005.K次取反后最大化的数组和.md
index 30718b13..020476a9 100644
--- a/problems/1005.K次取反后最大化的数组和.md
+++ b/problems/1005.K次取反后最大化的数组和.md
@@ -110,15 +110,16 @@ class Solution {
 	int len = nums.length;	    
 	for (int i = 0; i < len; i++) {
 	    //从前向后遍历，遇到负数将其变为正数，同时K--
-	    if (nums[i] < 0 && k > 0) {
+	    if (nums[i] < 0 && K > 0) {
 	    	nums[i] = -nums[i];
-		k--;
+	    	K--;
 	    }
 	}
 	// 如果K还大于0，那么反复转变数值最小的元素，将K用完
-	if (k % 2 == 1) nums[len - 1] = -nums[len - 1];
-	
+
+	if (K % 2 == 1) nums[len - 1] = -nums[len - 1];
 	return Arrays.stream(nums).sum();
+
     }
 }
 ```