Leetcode 缺失的第一个正整数

题目意思是找出第一个没出现的最小正整数。

Explanation:

  1. Move Numbers to Correct Positions:

    • The idea is to place each number in its corresponding index. For example, 1 should be at index 0, 2 should be at index 1, and so on. This is done using a while loop to swap the elements until all valid numbers (those within the range 1 to n) are in their respective positions.
  2. Find the First Missing Positive:

    • After the first step, iterate through the array. The first position where the element is not equal to i + 1 is the smallest missing positive integer.
  3. Return n + 1 if all numbers are in correct places:

    • If all numbers are in their correct places, the smallest missing positive integer must be n + 1.

Time Complexity:

  • The time complexity is O ( n ) O(n) O(n) because each element is swapped at most once.

Space Complexity:

  • The space complexity is O ( 1 ) O(1) O(1) since we are using constant extra space.
cpp 复制代码
class Solution {
public:
    int firstMissingPositive(vector<int>& nums) {
        int n = nums.size(); //由于数组下标是从0开始,所以值为 n 的元素的下标按顺序是 n - 1
        //例如1的下标是0,2的下标是1...
        for(int i = 0; i < n; i++) {
            //仅当当前元素值的范围介于[1,n]之间,并且它所该移动到的位置上的元素不相等时我们移动它到这个位置
            //值为 nums[i] 的元素按顺序排列的下标是 nums[i] - 1
            while(nums[i] > 0 && nums[i] <=n && nums[i] != nums[nums[i] - 1]) {
                swap(nums[i], nums[nums[i] - 1]);
            }
        }

        //然后,我们遍历数组,当下标 i 对应的值不等于 i + 1 时,返回 i + 1
        for(int i = 0; i < n; i++) {
            if(nums[i] != i + 1) {
                return i + 1;
            }
        }
        //如果在上面的循环中并没有return,说明数组所以元素值被排列成了 1,2,...,n
        return n + 1;
    }
};
相关推荐
梭七y2 小时前
【力扣hot100题】(063)搜索二维矩阵
算法·leetcode·职场和发展
@蓝莓果粒茶3 小时前
LeetCode第131题_分割回文串
开发语言·前端·算法·leetcode·职场和发展·c#·.net
雾里看山3 小时前
算法思想之滑动窗口(一)
算法·leetcode·推荐算法
梭七y3 小时前
【力扣hot100题】(034)LRU缓存
leetcode·缓存·哈希算法
alphaTao7 小时前
LeetCode 每日一题 2025/3/31-2025/4/6
算法·leetcode
禾小西9 小时前
Java 逐梦力扣之旅_[204. 计数质数]
java·算法·leetcode
LuckyLay9 小时前
LeetCode算法题(Go语言实现)_32
算法·leetcode·golang
ゞ 正在缓冲99%…9 小时前
leetcode295.数据流的中位数
java·数据结构·算法·leetcode·
爪娃侠9 小时前
LeetCode热题100记录-【二叉树】
linux·算法·leetcode
独好紫罗兰11 小时前
洛谷题单3-P1720 月落乌啼算钱(斐波那契数列)-python-流程图重构
开发语言·算法·leetcode