16. 3Sum Closest

2019/11/05 Leetcode

16. 3Sum Closest

Tags: ‘Array’, ‘Two Pointers’

Given an array nums of n integers and an integer target, find three integers in nums such that the sum is closest to target. Return the sum of the three integers. You may assume that each input would have exactly one solution.

Example:

Given array nums = [-1, 2, 1, -4], and target = 1.

The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).

Solution

类似 15 3Sum, 先排序再左右夹逼。 O(n2) O(1)

public int threeSumClosest(int[] nums, int target) {
    if (nums == null || nums.length == 0) return 0;
    if (nums.length <= 3) return Arrays.stream(nums).sum();
    Arrays.sort(nums);
    
    int minGap = Integer.MAX_VALUE;
    int result = 0;
    
    for (int i = 0; i < nums.length - 1; i++) {
        if (i > 0 && nums[i] == nums[i-1]) continue;
        
        int lo = i + 1, hi = nums.length - 1;
        while (lo < hi) {
            int sum = nums[i] + nums[lo] + nums[hi];
            int gap = Math.abs(target - sum);
            if (gap < minGap) {
                minGap = gap;
                result = sum;
            }
            if (sum == target) {
                break;
            } else if (sum < target) {
                lo++;
            } else {
                hi--;
            }
        }
    }
    return result;
}

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