(2) I feel like I haven’t learned anything today, board

//所谓的原地算法，其实就是修改数据，将数据成倍修改，跟状态数组的原理不就是一样的么。。
class Solution {
    
    
public:
    vector<int> findDisappearedNumbers(vector<int>& nums) {
    
    
        int n = nums.size();
        for (auto& num : nums) {
    
    
            int x = (num - 1) % n;
            nums[x] += n;
        }
        vector<int> ret;
        for (int i = 0; i < n; i++) {
    
    
            if (nums[i] <= n) {
    
    
                ret.push_back(i + 1);
            }
        }
        return ret;
    }
};

In this question, subtracting n, and then filtering the numbers greater than or equal to 0 must be correct, but the experiment actually showed a runtime error. This may be the problem of the subject itself.

Reorganize the matrix template

class Solution {
    
    
public:
    vector<vector<int>> matrixReshape(vector<vector<int>>& nums, int r, int c) {
    
    
        int m = nums.size();//行数目
        int n = nums[0].size();//列的数目
        if (m * n != r * c) {
    
    //若不相等则不可能
            return nums;
        }
        vector<vector<int>> ans(r, vector<int>(c));//答案vector
        for (int x = 0; x < m * n; ++x) {
    
    
            ans[x / c][x % c] = nums[x / n][x % n];//
        }
        return ans;
    }
};