diff --git a/problems/0056.合并区间.md b/problems/0056.合并区间.md
index 34d8dd82..7fe7c3d0 100644
--- a/problems/0056.合并区间.md
+++ b/problems/0056.合并区间.md
@@ -136,24 +136,38 @@ public:
 
 ### Java 
 ```java
+
+/**
+时间复杂度 ： O(NlogN) 排序需要O(NlogN)
+空间复杂度 ： O(logN)  java 的内置排序是快速排序 需要 O(logN)空间
+
+*/
 class Solution {
     public int[][] merge(int[][] intervals) {
         List<int[]> res = new LinkedList<>();
-        Arrays.sort(intervals, (o1, o2) -> Integer.compare(o1[0], o2[0]));
-
+        //按照左边界排序
+        Arrays.sort(intervals, (x, y) -> Integer.compare(x[0], y[0]));
+        //initial start 是最小左边界
         int start = intervals[0][0];
+        int rightmostRightBound = intervals[0][1];
         for (int i = 1; i < intervals.length; i++) {
-            if (intervals[i][0] > intervals[i - 1][1]) {
-                res.add(new int[]{start, intervals[i - 1][1]});
+            //如果左边界大于最大右边界
+            if (intervals[i][0] > rightmostRightBound) {
+                //加入区间 并且更新start
+                res.add(new int[]{start, rightmostRightBound});
                 start = intervals[i][0];
+                rightmostRightBound = intervals[i][1];
             } else {
-                intervals[i][1] = Math.max(intervals[i][1], intervals[i - 1][1]);
+                //更新最大右边界
+                rightmostRightBound = Math.max(rightmostRightBound, intervals[i][1]);
             }
         }
-        res.add(new int[]{start, intervals[intervals.length - 1][1]});
+        res.add(new int[]{start, rightmostRightBound});
         return res.toArray(new int[res.size()][]);
     }
 }
+
+}
 ```
 ```java
 // 版本2