lintcode_59. 最接近的三数之和

Posted 2020-10-17

给一个包含 n 个整数的数组 S, 找到和与给定整数 target 最接近的三元组，返回这三个数的和。

样例

例如 S = [-1, 2, 1, -4] and target = 1. 和最接近 1 的三元组是 -1 + 2 + 1 = 2.

class Solution:
    """
    @param: numbers: Give an array numbers of n integer
    @param: target: An integer
    @return: return the sum of the three integers, the sum closest target.
    """
    def threeSumClosest(self, numbers, target):
        # write your code here
        result = sum(numbers[:3]) -target
        
        for i in range(len(numbers)-2):
            for j in range(i+1,len(numbers)-1):
                for m in range(j+1,len(numbers)):
                    tmp = numbers[i]+numbers[j]+numbers[m]-target
                    if abs(result) > abs(tmp):
                        result = tmp
        return result+target

时间复杂度o（n^3）

九章算法参考：

class Solution:
    """
    @param numbers: Give an array numbers of n integer
    @param target : An integer
    @return : return the sum of the three integers, the sum closest target.
    """
    def threeSumClosest(self, numbers, target):
        numbers.sort()
        ans = None
        for i in range(len(numbers)):
            l, r = i + 1, len(numbers) - 1
            while (l < r):                    
                sum = numbers[l] + numbers[r] + numbers[i]
                if ans is None or abs(sum- target) < abs(ans - target):
                    ans = sum
                if sum <= target:
                    l = l + 1
                else:
                    r = r - 1
        return ans

有点类似背包问题，放缩的比较好，提高了效率