https://leetcode-cn.com/problems/3sum
var threeSum = function (nums) {
let res = [];
const len = nums.length;
nums.sort((a,b) => a - b);
for (let i = 0; i < len; i++) {
if (nums[i] > 0) break; // 如果当前数字大于0,则三数之和一定大于0,所以结束循环
if (i > 0 && nums[i] == nums[i - 1]) continue;
let L = i + 1;
let R = len - 1;
while (L < R) {
const sum = nums[i] + nums[L] + nums[R];
if (sum == 0) {
res.push([nums[i],nums[L],nums[R]]);
while (L < R && nums[L] == nums[L+1]) L++; // 去重
while (L < R && nums[R] == nums[R-1]) R--; // 去重
L++;
R--;
} else if (sum < 0) {
L++
} else if (sum > 0) {
R--
}
}
}
return res;
}