[LeetCode]448. Find All Numbers Disappeared in an Array

[LeetCode]448. Find All Numbers Disappeared in an Array

题目描述

思路

使用map保存应该出现的数，然后遍历数组，把出现过的数在map中做标记，然后输入map中未被标记的数

代码

class Solution {
public:
    vector<int> findDisappearedNumbers(vector<int>& nums) {
        vector<int> res = {};
        unordered_map<int, int> normal;

        for (int i = 0; i < nums.size(); ++i){
            normal[i + 1] = 1;
        }
        for (int &p : nums){
            normal[p] = 0;
        }
        for (auto &p : normal){
            if (p.second){
                res.push_back(p.first);
            }
        }
        return res;
    }
};

思路 空间复杂度O(1)

对出现过的数标记为负，在对应位置上数字为正，则该数未出现，输出对应位置

代码

class Solution {
public:
    vector<int> findDisappearedNumbers(vector<int>& nums) {
        vector<int> res = {};
        for (int i = 0; i < nums.size(); ++i){
            int m = abs(nums[i]) - 1;
            nums[m] = nums[m] > 0 ? -nums[m] : nums[m];
        }
        for (int i = 0; i < nums.size(); ++i) {
            if (nums[i] > 0) {
                res.push_back(i + 1);
            }
        }
        return res;
    }
};