Basic practice of Blue Bridge Cup - shape retrieval of matrix (C language)

Catalog

 

One 、 Problem description ：

Two 、 Their thinking

3、 ... and 、 Code

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One 、 Problem description ：

To take a number from a loop is to take a number along the edge of a matrix , If the current direction of countless or have taken , Turn left 90 degree . It starts at the top left corner of the matrix , Direction down .

Input format ：

　　 The first line of input is no more than 200 The positive integer m, n, The rows and columns that represent the matrix . Next m Every line n It's an integer , To represent this matrix .

Output format ：

　　 There is only one line of output , common mn Number , The result of taking data for the input matrix . Numbers are separated by a space , There should be no extra space at the beginning and end of the line .

The sample input 1：

3  3

1   2   3

4   5   6

7   8   9

Sample output 1：

1 4 7 8 9 6 3 2 5

The sample input 2：

3  2

1   2

3   4

5   6 

The sample input 2：

1  3  5  6  4  2

Two 、 Their thinking

      This topic examines two-dimensional arrays and circular structures , It belongs to the basic topic . The topic mainly stipulates a rule of data retrieval , That is, counter clockwise, take data in turn according to the shape and output . Because there are many kinds of matrix shapes , It can be roughly divided into two kinds ：1. A matrix with equal rows and columns 2. Matrix with unequal rows and columns . And it should be considered that some small matrices may be completed in less than one cycle , Such as a matrix with three rows and two columns , Just finish down , towards the right , Up again, the data retrieval is completed , There is no complete circle . The complete circle should be ： Next —> Right —> On —> Left

    So the code should look at the problem in a general way , That is, get the general solution of the problem instead of the special solution . In the following code, each step of the operation is while In the circulatory system &&count Its function is to judge whether all the numbers have been taken , Whether to perform the next step of data retrieval .

    Because the comments in the code are already very detailed , No more details here .

3、 ... and 、 Code

// Based on practice ： Return to the shape of the data 
#include<stdio.h>
int main(){
	int m,n,count;
	int i,j;
	// Parameter description ：m For the line n Column ,count Is the total number of matrix elements  
	scanf("%d%d",&m,&n);
	count=m*n;
	int arr[m][n];
	// Next, initialize the matrix 
	for(i=0;i<m;i++)
	   for(j=0;j<n;j++)
	      scanf("%d",&arr[i][j]);
	// Now let's start the operation of shape retrieval ： Down , towards the right , Up , towards the left ...... Cyclic repetition 
	i=0;j=0;// there i,j Respectively represent the coordinate positions of elements in the matrix (i,j)
	int circle=0;//circle Represents the number of cycles of loop retrieval 
	while(count){
		// Take the number down : The line is changing , The column does not change  
		while(i<m-circle&&count){
			if(i==0&&j==0){
			   printf("%d",arr[0][0]);
			   i++;// Easily overlooked points ： Print out the first element in the upper left corner , Be sure to move the line to the next line ！ 
			}
			else
			  printf(" %d",arr[i++][j]);
			count--;// Number of each print , Make total count Minus one  
		}
		i--;// Because after printing the last row element of the column ,i Or automatically add 1, It will be crossed ,
		    // so i-- Bring it back to the circle The last line of circle fetching down  
		j++;// After the downward data retrieval , Add one to the number of columns , Ready to fetch right 
		while(j<n-circle&&count){
			printf(" %d",arr[i][j++]);
			count--;
		} 
		j--;// Empathy  
		i--;// Prepare to fetch up 
		while(i>=circle&&count){
			printf(" %d",arr[i--][j]);
			count--;
		}
		i++;// Empathy  
		j--;// Ready to fetch left 
		while(j>circle&&count){
			printf(" %d",arr[i][j--]);
			count--;
		} 
		j++;// Empathy  
		i++;// The loop takes one round and ends , The next loop of loop retrieval starts from the second element on the right diagonal ...... 
		circle++;// The lap ends , Turns plus one  
	} 
	return 0;
} 

Running results ：

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