Update Leetcode 题解.md

maxSubArray优化代码，没有必要初始化一个n长度的数组

notes/Leetcode 题解.md

@@ -2379,13 +2379,11 @@ class NumArray {
 
 ```java
 public int maxSubArray(int[] nums) {
-    int n = nums.length;
-    int[] sum = new int[n];
-    sum[0] = nums[0];
-    int max = sum[0];
-    for(int i = 1; i < n; i++){
-        sum[i] = (sum[i-1] > 0 ? sum[i-1] : 0) + nums[i];
-        max = Math.max(max, sum[i]);
+    int max = nums[0];
+    int oldsum = nums[0];
+    for (int i = 1; i < nums.length; i++) {
+        oldsum = (oldsum > 0 ? oldsum: 0) + nums[i];
+        max = Math.max(max, oldsum);
     }
     return max;
 }