378. 有序矩陣中第K小的元素(二分，歸併排序，優先隊列)

class Solution {
public:
    int kthSmallest(vector<vector<int>>& matrix, int k) {
        int n=matrix.size();
        vector<int> temp(n*n,0);
        int i,j,ki;
        ki=0;
        for(i=0;i<n;i++)
        for(j=0;j<n;j++)
        temp[ki++]=matrix[i][j];
        sort(temp.begin(),temp.end());
        return temp[k-1];
    }
};

歸併排序

class Solution {
public:
    int kthSmallest(vector<vector<int>>& matrix, int k) {
        int n=matrix.size();
        vector<int> res(n*n,0);
        int * l=& matrix[0][0];
        for(int st=0;st<n;st++)
            res[st]=*(l++);
        int len=0;
        int t=1;
        while(t<n){
        
            len=len+n;
            int left[len];
            for(int m=0;m<len;m++)
                left[m]=res[m];
            int *right=& matrix[t][0];
            int ki=0,i=0,j=0;
            while(i<len&& j<n){
                if(left[i]<right[j]){
                    res[ki++]=left[i];
                    i++;
                }
                else{
                    res[ki++]=right[j];
                    j++;
                }
            }
            while(i<len) res[ki++]=left[i++];
            while(j<n) res[ki++]=right[j++];
            t++;
        }
        return res[k-1];
    }
};
`

class Solution {
public:
    int numOfLeMid(vector<vector<int>> & matrix,int mid){
        int n=matrix.size();
        int i=n-1,j=0;
        int sum=0;
        while(i>=0&&j<n){
            if(matrix[i][j]<=mid) {
                sum+=i+1;
                j++;
            }
            else
                i--;
        }
        return sum;
    }
    int kthSmallest(vector<vector<int>>& matrix, int k) {
        int L=matrix[0][0];
        int n=matrix.size();
        int R=matrix[n-1][n-1];
        while(L<R){
            int mid=L+((R-L)>>2);
            if(numOfLeMid(matrix,mid)<k)
                L=mid+1;
            else
                R=mid;
        }
        return L;
    }
};

class Solution {
public:
   
    int kthSmallest(vector<vector<int>>& matrix, int k) {
       
        int n=matrix.size();

        struct point{
            int val,x,y;
            point(int val,int x,int y){
                this->val=val;
                this->x=x;
                this->y=y;
            }
            bool operator >(const point &a) const { return this->val>a.val;}
        };
        priority_queue<point,vector<point>,greater<point>> que;

        for(int i=0;i<n;i++){
            point a (matrix[0][i],0,i);
            que.push(a);
        }
        for(int j=0;j<k-1;j++){
            point temp=que.top();
            que.pop();
            if(temp.x<n-1) que.push(point   (matrix[temp.x+1][temp.y],temp.x+1,temp.y));
        }
        return que.top().val;
    }
};

堆排序

class Solution {
public:
   
    int kthSmallest(vector<vector<int>>& matrix, int k) {
       
        int n=matrix.size();

        struct point{
            int val;
            point(int val){
                this->val=val;
            }
            bool operator >(const point &a) const { return this->val>a.val;}
        };
        priority_queue<point,vector<point>,greater<point>> que;
      
        vector<int>res(n*n,0);
        int i,j;
        for(i=0;i<n;i++){
            for (j=0;j<n;j++)
            que.push(point   (matrix[i][j]));
        }
        for(j=0;j<k-1;j++)
            que.pop();
        return que.top().val;
    }
};

斜體樣式