Find orientation of a pattern in a matrix in C++

In this problem, we are given a matrix consisting of character values that make a pattern, we are also given a pattern to be found. Our task is to find the orientation (horizontal or vertical) of a pattern in a matrix.

Let’s take an example to understand the problem,

Input

mat[][] = {
   { r, a, m },
   {a, m, c},
   {w, f, t}
}
Patern : raw

Output

vertical

Solution Approach

A simple solution to the problem is by searching the M sized pattern in all the N rows of the matrix. This solution is ok but a more effective solution to the problem is by using the KML pattern matching algorithm for all rows and columns of the matrix.

Program to illustrate the working of our solution,

Example

Live Demo

#include<bits/stdc++.h>
using namespace std;
#define N 3
void calcLpsValues(char *pat, int M, int *lps) {
   int len = 0;
   int i = 1;
   lps[0] = 0;
   while (i < M) {
      if (pat[i] == pat[len]) {
         len++;
         lps[i++] = len;
      } else {
         if (len != 0)
            len = lps[len - 1];
         else
            lps[i++] = 0;
      }
   }
}
int searchPattern(char *pat, char *txt) {
   int M = strlen(pat);
   int *lps = (int *)malloc(sizeof(int)*M);
   int j = 0;
   calcLpsValues(pat, M, lps);
   int i = 0;
   while (i < N) {
      if (pat[j] == txt[i]) {
         j++;
         i++;
      }
      if (j == M)
         return 1;
      else if (i < N && pat[j] != txt[i]) {
         if (j != 0)
            j = lps[j - 1];
         else
            i = i + 1;
      }
   }
   return 0;
}
void findPatternOrientation(char mat[][N], char *pat) {
   char *col = (char*) malloc(N);
   for (int i = 0; i < N; i++) {
      if (searchPattern(pat, mat[i])) {
         cout<<"horizontal";
         return;
      }
      for (int j = 0; j < N; j++)
         col[j] = *(mat[j] + i);
      if (searchPattern(pat, col))
         cout<<"vertical";
   }
}
int main() {
   char mat[N][N] = {{'r', 'a', 'm'},
   {'a', 'm', 'c'},
   {'w', 'f', 't'}};
   char pattern[] = "raw";
   cout<<"The orientation of the pattern in matrix is ";
   findPatternOrientation(mat, pattern);
   return 0;
}

Output

The orientation of the pattern in matrix is vertical

Sudhir sharma

Published on 16-Mar-2021 04:46:44

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