Update 0018.四数之和.md

add 剪枝 to the second for loop

Author: stevenleon99

problems/0018.四数之和.md

@@ -262,6 +262,11 @@ class Solution {
             
             for (int j = i + 1; j < nums.length; j++) {
 
+		// nums[i]+nums[j] > target 直接返回, 剪枝操作
+		            if (nums[i]+nums[j] > 0 && nums[i]+nums[j] > target) {
+		                return result;
+		            }
+
                 if (j > i + 1 && nums[j - 1] == nums[j]) {  // 对nums[j]去重
                     continue;
                 }