📜  所有子矩阵的按位与之和

📅  最后修改于: 2021-09-17 06:45:42             🧑  作者: Mango

给定一个NxN矩阵,任务是找到其所有矩形子矩阵的按位与的总和。

例子:

Input : arr[][] = {{1, 1, 1},
                   {1, 1, 1},
                   {1, 1, 1}}
Output : 36
Explanation: All the possible submatrices will have AND value 1.
Since, there are 36 submatrices in total, ans = 36

Input : arr[][] = {{9, 7, 4},
                   {8, 9, 2},
                   {11, 11, 5}}
Output : 135 

先决条件:全1的二进制矩阵的矩形子矩阵的数量。
朴素的解决方案:一个简单的解决方案是生成所有子矩阵并为每个子矩阵找到所需的 AND。这种方法的时间复杂度为 O(N 6 )。

有效的方法:为了更好的理解,我们假设一个元素的任何位都由变量’i’表示,变量’sum’用于存储最终的总和。
这里的想法是,我们将尝试找到第 i位集的 AND 值(具有按位和(&)的子矩阵)的数量。让我们假设,有 ‘S i个第i 位设置的子矩阵。对于i 位,总和可以更新为sum += (2 i * S i )
对于每个位“i”,如果设置了 arr[R][C] 的i 位,则创建一个布尔矩阵set_bit将“1”存储在索引 (R, C) 处。否则,它存储“0”。然后,对于这个布尔数组,我们尝试找到全为 1s(S i ) 的矩形子矩阵的数量。对于i 位,最终和将更新为:

sum += 2i * Si

下面是上述方法的实现:

C++
// C++ program to find sum of Bit-wise AND
// of all submatrices
 
#include 
#include 
 
using namespace std;
 
#define n 3
 
// Function to find prefix-count for each row
// from right to left
void findPrefixCount(int p_arr[][n], bool set_bit[][n])
{
    for (int i = 0; i < n; i++) {
        for (int j = n - 1; j >= 0; j--) {
            if (!set_bit[i][j])
                continue;
 
            if (j != n - 1)
                p_arr[i][j] += p_arr[i][j + 1];
 
            p_arr[i][j] += (int)set_bit[i][j];
        }
    }
}
 
// Function to find the number of submatrices
// with all 1s
int matrixAllOne(bool set_bit[][n])
{
    // Array to store required prefix count of 1s from
    // right to left for boolean array
    int p_arr[n][n] = { 0 };
 
    findPrefixCount(p_arr, set_bit);
 
    // Variable to store the final answer
    int ans = 0;
 
    // For each index of a column, determine the number
    // of sub-matrices starting from that index
    // and has all 1s
    for (int j = 0; j < n; j++) {
        int i = n - 1;
 
        // Stack to store elements and the count
        // of the numbers they popped
        // First part of pair is value of inserted element
        // Second part is count of the number of elements
        // pushed before with a greater value
        stack > q;
 
        // variable to store the number of submatrices
        // with all 1s
        int to_sum = 0;
 
        while (i >= 0) {
            int c = 0;
            while (q.size() != 0 and q.top().first > p_arr[i][j]) {
                to_sum -= (q.top().second + 1) * (q.top().first - p_arr[i][j]);
                c += q.top().second + 1;
                q.pop();
            }
 
            to_sum += p_arr[i][j];
            ans += to_sum;
 
            q.push({ p_arr[i][j], c });
            i--;
        }
    }
 
    return ans;
}
 
// Function to find the sum of Bitwise-AND
// of all submatrices
int sumAndMatrix(int arr[][n])
{
    int sum = 0;
 
    int mul = 1;
 
    for (int i = 0; i < 30; i++) {
        // matrix to store the status
        // of ith bit of each element
        // of matrix arr
        bool set_bit[n][n];
 
        for (int R = 0; R < n; R++)
            for (int C = 0; C < n; C++)
                set_bit[R][C] = ((arr[R][C] & (1 << i)) != 0);
 
        sum += (mul * matrixAllOne(set_bit));
 
        mul *= 2;
    }
 
    return sum;
}
 
// Driver Code
int main()
{
    int arr[][n] = { { 9, 7, 4 },
                     { 8, 9, 2 },
                     { 11, 11, 5 } };
 
    cout << sumAndMatrix(arr);
 
    return 0;
}


Java
// Java program to find sum of Bit-wise AND
// of all submatrices
import java.util.*;
 
class GFG
{
 
static int n = 3;
 
// Function to find prefix-count for 
// each row from right to left
static void findPrefixCount(int p_arr[][],
                            boolean set_bit[][])
{
    for (int i = 0; i < n; i++)
    {
        for (int j = n - 1; j >= 0; j--)
        {
            if (!set_bit[i][j])
                continue;
 
            if (j != n - 1)
                p_arr[i][j] += p_arr[i][j + 1];
 
            p_arr[i][j] += (set_bit[i][j]) ? 1 : 0;
        }
    }
}
static class pair
{
    int first,second;
    pair(){}
     
    pair(int a, int b)
    {
        first = a;
        second = b;
    }
}
 
// Function to find the number of
// submatrices with all 1s
static int matrixAllOne(boolean set_bit[][])
{
    // Array to store required prefix count of 1s from
    // right to left for boolean array
    int p_arr[][] = new int[n][n];
     
    for(int i = 0; i < n; i++)
        for(int j = 0; j < n;j++)
            p_arr[i][j] = 0;
     
    findPrefixCount(p_arr, set_bit);
 
    // Variable to store the final answer
    int ans = 0;
 
    // For each index of a column, determine the number
    // of sub-matrices starting from that index
    // and has all 1s
    for (int j = 0; j < n; j++)
    {
        int i = n - 1;
 
        // Stack to store elements and the count
        // of the numbers they popped
        // First part of pair is value of inserted element
        // Second part is count of the number of elements
        // pushed before with a greater value
        Stack q = new Stack();
 
        // variable to store the number of submatrices
        // with all 1s
        int to_sum = 0;
 
        while (i >= 0)
        {
            int c = 0;
            while (q.size() != 0 &&
                    q.peek().first > p_arr[i][j])
            {
                to_sum -= (q.peek().second + 1) *
                            (q.peek().first - p_arr[i][j]);
                c += q.peek().second + 1;
                q.pop();
            }
 
            to_sum += p_arr[i][j];
            ans += to_sum;
 
            q.push(new pair( p_arr[i][j], c ));
            i--;
        }
    }
    return ans;
}
 
// Function to find sum of Bitwise-OR of
// all submatrices
static int sumAndMatrix(int arr[][])
{
    int sum = 0;
 
    int mul = 1;
 
    for (int i = 0; i < 30; i++)
    {
        // matrix to store the status
        // of ith bit of each element
        // of matrix arr
        boolean set_bit[][] = new boolean[n][n];
 
        for (int R = 0; R < n; R++)
            for (int C = 0; C < n; C++)
                set_bit[R][C] = ((arr[R][C] & (1 << i)) != 0);
 
        sum += (mul * matrixAllOne(set_bit));
 
        mul *= 2;
    }
    return sum;
}
 
// Driver Code
public static void main(String args[])
{
    int arr[][] = { { 9, 7, 4 },
                    { 8, 9, 2 },
                    { 11, 11, 5 } };
 
    System.out.println( sumAndMatrix(arr));
}
}
 
// This code is contributed by Arnab Kundu


Python3
# Python3 program to find sum of
# Bitwise-AND of all submatrices
 
# Function to find prefix-count for
# each row from right to left
def findPrefixCount(p_arr, set_bit):
 
    for i in range(0, n):
        for j in range(n - 1, -1, -1):
 
            if not set_bit[i][j]:
                continue
            if j != n - 1:
                p_arr[i][j] += p_arr[i][j + 1]
 
            p_arr[i][j] += int(set_bit[i][j])
 
# Function to create a boolean matrix
# set_bit which stores ‘1’ at an index
# (R, C) if ith bit of arr[R][C] is set.
def matrixAllOne(set_bit):
 
    # Array to store prefix count of zeros
    # from right to left for boolean array
    p_arr = [[0 for i in range(n)]
                for j in range(n)]
 
    findPrefixCount(p_arr, set_bit)
 
    # Variable to store the final answer
    ans = 0
 
    # For each index of a column we
    # will try to determine the number
    # of sub-matrices starting from
    # that index and has all 1s
    for j in range(0, n):
 
        i = n - 1
         
        # stack to store elements and the
        # count of the numbers they popped
 
        # First part of pair will be the
        # value of inserted element.
        # Second part will be the count
        # of the number of elements pushed
        # before with a greater value
        q = []
 
        # Variable to store the number
        # of submatrices with all 0s
        to_sum = 0
         
        while i >= 0:
 
            c = 0
            while (len(q) != 0 and
                   q[-1][0] > p_arr[i][j]):
 
                to_sum -= ((q[-1][1] + 1) *
                           (q[-1][0] - p_arr[i][j]))
 
                c += q.pop()[1] + 1
 
            to_sum += p_arr[i][j]
            ans += to_sum
 
            q.append((p_arr[i][j], c))
            i -= 1
 
    # Return the final answer
    return ans
 
# Function to find sum of
# Bitwise-AND of all submatrices
def sumAndMatrix(arr):
 
    Sum, mul = 0, 1
    for i in range(0, 30):
     
        # matrix to store the status
        # of ith bit of each element
        # of matrix arr
        set_bit = [[False for i in range(n)]
                          for j in range(n)]
 
        for R in range(0, n):
            for C in range(0, n):
                set_bit[R][C] = ((arr[R][C] &
                                 (1 << i)) != 0)
 
        Sum += (mul * matrixAllOne(set_bit))
        mul *= 2
 
    return Sum
 
# Driver Code
if __name__ == "__main__":
     
    n = 3
    arr = [[9, 7, 4],
        [8, 9, 2],
        [11, 11, 5]]
 
    print(sumAndMatrix(arr))
 
# This code is contributed by Rituraj Jain


C#
// C# program to find sum of Bit-wise AND
// of all submatrices
using System;
using System.Collections.Generic;
 
class GFG
{
 
static int n = 3;
 
// Function to find prefix-count for
// each row from right to left
static void findPrefixCount(int [,]p_arr,
                            bool [,]set_bit)
{
    for (int i = 0; i < n; i++)
    {
        for (int j = n - 1; j >= 0; j--)
        {
            if (!set_bit[i, j])
                continue;
 
            if (j != n - 1)
                p_arr[i, j] += p_arr[i, j + 1];
 
            p_arr[i, j] += (set_bit[i, j]) ? 1 : 0;
        }
    }
}
public class pair
{
    public int first,second;
    public pair(){}
     
    public pair(int a, int b)
    {
        first = a;
        second = b;
    }
}
 
// Function to find the number of
// submatrices with all 1s
static int matrixAllOne(bool [,]set_bit)
{
    // Array to store required prefix count of 1s from
    // right to left for boolean array
    int [,]p_arr = new int[n, n];
     
    for(int i = 0; i < n; i++)
        for(int j = 0; j < n;j++)
            p_arr[i, j] = 0;
     
    findPrefixCount(p_arr, set_bit);
 
    // Variable to store the final answer
    int ans = 0;
 
    // For each index of a column, determine the number
    // of sub-matrices starting from that index
    // and has all 1s
    for (int j = 0; j < n; j++)
    {
        int i = n - 1;
 
        // Stack to store elements and the count
        // of the numbers they popped
        // First part of pair is value of inserted element
        // Second part is count of the number of elements
        // pushed before with a greater value
        Stack q = new Stack();
 
        // variable to store the number of submatrices
        // with all 1s
        int to_sum = 0;
 
        while (i >= 0)
        {
            int c = 0;
            while (q.Count != 0 &&
                    q.Peek().first > p_arr[i,j])
            {
                to_sum -= (q.Peek().second + 1) *
                            (q.Peek().first - p_arr[i,j]);
                c += q.Peek().second + 1;
                q.Pop();
            }
 
            to_sum += p_arr[i,j];
            ans += to_sum;
 
            q.Push(new pair( p_arr[i,j], c ));
            i--;
        }
    }
    return ans;
}
 
// Function to find sum of Bitwise-OR of
// all submatrices
static int sumAndMatrix(int [,]arr)
{
    int sum = 0;
 
    int mul = 1;
 
    for (int i = 0; i < 30; i++)
    {
        // matrix to store the status
        // of ith bit of each element
        // of matrix arr
        bool [,]set_bit = new bool[n,n];
 
        for (int R = 0; R < n; R++)
            for (int C = 0; C < n; C++)
                set_bit[R, C] = ((arr[R, C] & (1 << i)) != 0);
 
        sum += (mul * matrixAllOne(set_bit));
 
        mul *= 2;
    }
    return sum;
}
 
// Driver Code
public static void Main(String []args)
{
    int [,]arr = { { 9, 7, 4 },
                    { 8, 9, 2 },
                    { 11, 11, 5 } };
 
    Console.WriteLine(sumAndMatrix(arr));
}
}
 
// This code contributed by Rajput-Ji


Javascript


输出:
135

时间复杂度:O(N 2 )。