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export default function threeSum(nums: number[]): number[][] {    if (nums.length < 3) {        return [];    }
    nums.sort((a, b) => a - b);    const cache = new Set<string>();
    const ans: number[][] = [];
    const len = nums.length;
    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
        let L = i + 1;        let R = len - 1;        while (L < R) {            const sum = nums[i] + nums[L] + nums[R];            if (sum == 0) {                const a = [nums[i], nums[L], nums[R]];                const key = a.join("");                if (!cache.has(key)) {                    cache.add(key);                    ans.push(a);                }
                L++;                R--;            } else if (sum < 0) L++;            else if (sum > 0) R--;        }    }
    return ans;}