题目来源
https://leetcode.com/problems/first-missing-positive/
Given an unsorted integer array, find the first missing positive integer.
For example,
Given [1,2,0] return 3,
and [3,4,-1,1] return 2.
Your algorithm should run in O(n) time and uses constant space.
题意分析
Input:a list with many numbers
Output:the first missing positive number
Conditions:最小的missing 正整数，注意要0（n）级别的算法
题目思路
利用字典去做，因为字典查询是0（n）的，不过会使用0（n）的空间，AC了，但是网上说要用triky，可能是leecode评测放宽了……以后再回来看看
AC代码（Python）
1 _author_ = "YE" 2 # -*- coding:utf-8 -*- 3 4 class Solution(object): 5 def firstMissingPositive(self, nums): 6 """ 7 :type nums: List[int] 8 :rtype: int 9 """ 10 len1 = len(nums) 11 if len1 == 0: 12 return 1 13 dic = {} 14 for num in nums: 15 if num > 0: 16 dic[num] = num 17 for i in range(1, len1 + 1): 18 if dic.get(i, -1) == -1: 19 return i 20 return len1 + 1
[LeetCode]题解（python）：041-First Missing Positive
原文：http://www.cnblogs.com/loadofleaf/p/5042849.html