15. 三数之和

15. 三数之和

左右排除法

if (nums[i] > 0) break; 大于0

if (i > 0 && nums[i] == nums[i - 1]) continue; 去除重复操作

while (left < right) { 左右浓缩

var threeSum = function (nums) {
    var res = [];
    var len = nums.length;
    if (nums == null || len < 3) return res;
    nums.sort((a, b) => a - b);
    for (var i = 0; i < len; i++) {
        if (nums[i] > 0) break;
        if (i > 0 && nums[i] == nums[i - 1]) continue;
        var left = i + 1;
        var right = len - 1;
        while (left < right) {
            var sum = nums[i] + nums[left] + nums[right];
            if (sum == 0) {
                res.push([nums[i], nums[left], nums[right]]);
                while (left < right && nums[left] == nums[left + 1]) left++;
                while (left < right && nums[right] == nums[right - 1]) right--;
                left++;
                right--;
            } else if (sum < 0) {
                left++;
            } else if (sum > 0) {
                right--;
            }
        }
    }
    return res;
};