perf: a little tricky $15.3-sum (azl397985856#316)

* Update 15.3-sum

a trick to improve performence

* fix: code style

Co-authored-by: lucifer <azl397985856@gmail.com>

Author: zhangbotong

problems/15.3-sum.md

@@ -89,6 +89,8 @@ var threeSum = function(nums) {
   const list = [];
   nums.sort((a, b) => a - b);
   for (let i = 0; i < nums.length; i++) {
+    //nums is sorted,so it's impossible to have a sum = 0
+    if (nums[i] > 0) break;
     // skip duplicated result without set
     if (i > 0 && nums[i] === nums[i - 1]) continue;
     let left = i;