Data Structure Tutorial The third lesson algorithm and algorithm design requirements

the subject of this lesson: algorithm and algorithm design requirements

Teaching Purpose: to master the definition and characteristics of algorithm, the requirements of algorithm design

Teaching emphases: the characteristic of algorithm, the design requirement of algorithm

Teaching Difficulty: The requirement of algorithm design

Teaching Content:

Definition and characteristics of the algorithm

1. Definition:

Ispass (int num[4][4])

{int i,j;
for (i=0;i<4;i++)

for (j=0;j<4;j++)

if (num[i][j]!=i*4+j+1)/* An instruction, multiple operations * *

return 0;

return 1;
}/* above is a similar Huarong game to determine whether the game is the end of the algorithm * *

An algorithm is a description of a specific problem-solving step, which is a finite sequence of instructions, where each instruction represents one or more operations; In addition, an algorithm has the following five important features:

2, the algorithm of the five characteristics:

Have a poor sex	An algorithm must always (for any valid input value) end after a poor execution, and each step can be completed in a poor time;
Certainty	Each instruction in the algorithm must have the exact meaning, the reader does not produce two semantic when understanding. Under any condition, the algorithm has only one execution path, that is, only the same output can be obtained for the same input.
Feasibility	An algorithm can be done, that is, the operation described in the algorithm can be implemented through the implementation of the basic operation of a finite number of times to achieve.
Input	An algorithm has 0 or more inputs, which are taken from a collection of specific objects.
Output	An algorithm has one or more outputs. These outputs are quantities that have certain relationships with the input.

Cases:

poor	haha () {/*only A Joke,do nothing.*/ } Main () {printf (Please wait ...) You will know the day of the world ... "); while (1) haha (); }
deterministic	Flo At average (int *a,int num) {int I;long sum=0; for (i=0;i<num;i++) sum+=* (a++); return sum/num; } Main () {int score[10]={1,2,3,4,5,6,7,8,9,0}; printf ("%f", average (score,10); }
feasibility
	output	getsum (int num) { int i, sum=0; for (i=1;i<=num;i++) Sum+=i; }/* No output algorithm has no meaning,

Second, the requirements of algorithm design

1. Correctness

Four levels of correctness of the algorithm
program Contains no syntax errors.	max (int a,int b,int c) { if (a>b) {if (a>c) return C; else return A; } }
program can produce results that meet specification requirements for several sets of input data.	max (int a,int b,int c) { if (a>b) {if (a>c) return A; else return C; } }/* 8,6,7 *///* 9,3,2 */
program for carefully selected sets of typical, harsh, and difficult groups of inputs Data can be obtained to meet the specifications of the requirements of the results.	max (int a,int b,int c) { if (a>b) {if (a>c) return A; else return C; } Else {if (b>c) return B; else return C; } }
The program produces results that meet specification requirements for all legitimate input data.	 

2, readability

3, the robustness of

4. Efficiency and low storage demand

Efficiency refers to the execution time of an algorithm. For multiple algorithms that solve the same problem, the algorithm with short execution time is highly efficient.

Storage requirement refers to the maximum memory space needed in the algorithm execution.

Both are related to the size of the problem.

 	algorithm one	algorithm two
	max (int a,int b,int c) {if (a>b) {if (a>c) return A; else return C; } Else {if (b>c) return B; else return C; }/* eliminates the need for additional storage, only two comparisons */	1 The largest of the 00 integers	The same algorithm is difficult to write, difficult to read	max (int a[100] ) {int c,int i; C=A[0]; for (i=1;i<100;i++) if (a[i]>c) c=a[i]; return C; } /* A total of 102 integer spaces required/

Third, summary

1, the characteristics of the algorithm

2, the algorithm design requirements: Correctness, readability, robustness, efficiency and low storage requirements.