[C language] Character count statistics

Question description

Question source:Character count statistics_Niuke Question Ba_Niuke.com (nowcoder.com)

Write a function that counts the number of different characters contained in a string. The characters are in the ASCII code range (0~127, including 0 and 127). The newline represents the terminator and is not included in the characters. Those not within the scope will not be counted. Multiple identical characters are counted only once

For example, for the string abaca, there are three different characters a, b, and c, so the output is 3.

Data range: 1 ≤ n ≤ 500

Enter description:

Enter a line of string without spaces.

Output description:

Output the number of characters in the input string ranging from (0 to 127, including 0 and 127).

Example 1

enter:

abc

Output:

3

Example 2

enter:

aaa

Output:

1

Analysis of ideas

This question is not so much about counting the number of characters as it is about counting the types of characters. It’s like I gave you an array and asked you to find out how many numbers appear once in it.

Then there is actually more than one solution:

1. Create a new character array to store the characters that have appeared, and traverse the original string to find a new one and store it in an array.
2. After sorting the strings, iterate through the array and add 1 to the direct counter when encountering a new one.

But obviously the second one is simpler, so we use the second idea

---

First create an array and collect characters. No more talk about the old routine.

int main(){
    
    
    char str[501];
    gets(str);
    return 0;
}

Then we need to solve our sorting problem. You can write a sorting algorithm here, but here I recommend using the qsort function directly to save trouble and worry. Let us review it first. qsortfunction

---

void qsort (void* base, size_t num, size_t size,int (*compar)(const void*,const void*));

Return value: No return value, only the position pointed to bybase will be sorted

Parameter:base, pointing to the starting point of the data we want to sort

num, the number of data we want to sort

size, the size of the individual data we want to sort

compar, a function pointer, points to a size comparison function, used to tellqsort how to compare the size of the data you provide, where the parameters of this function are two< a i=2>, the return value is intconst void*

Suppose the followingcamparstatement

int compar (const void* p1, const void* p2);

When the return value< 0: The element pointed to by p1 will be placed in front of the element pointed by p2

Return= 0：p1Japanesep2Position not changed

When the return value> 0: The element pointed to by p1 will be placed after the element pointed to by p2

In fact, this return value will affect whether your sorting result is in forward or reverse order. If it does not meet expectations, just swap the positions.

---

So if we want to use the qsort function here, we need to know how many valid characters our string stores, so we write a simple loop for statistics

    int count = 0;
    while (str[count]) {
    
    
        count++;
    }

Then we need to write a function to compare sizes. Since the nature of characters is integer, we can actually directly return the difference between the two characters.

But here are a few points to note:

1. void*Type pointers must be type converted before they can be used
2. Don’t be confused by the return value here. Convert the pointer type to int*, otherwise the dereference will become access to 4 bytes
3. The type of parameters and the type of return value must correspond, includingconst

int cmp_char (const void* p1, const void* p2) {
    
    
    return *(char*)p1 - *(char*)p2;
}

Then we can callqsort to sort

qsort(str, count, 1, cmp_char);

Finally, we count the number of types of characters. We just start from the first one and compare it with the next character. If we find that they are not equal, let our counter increment.

Here are a few points to note:

1. Circulation cyclecount-1Next
2. The starting number of the counter should be1, because there must be a type of character at the beginning, and our comparison algorithm will not add the first type of character . From the perspective of the number of loops, when there is only one character, the loop is executedcount-1 times, which is 0 times, but there is actually one character

code show as below

    int num = 1;
    for (int i = 0; i < count - 1; i++) {
    
    
        if (str[i] != str[i + 1]) {
    
    
            num++;
        }
    }

Then finally print ournum

Code overview

#include <stdio.h>
#include <stdlib.h>

int cmp_char (const void* p1, const void* p2) {
    
    
    return *(char*)p1 - *(char*)p2;
}
int main() {
    
    
    char str[501];
    gets(str);
    int count = 0;
    while (str[count]) {
    
    
        count++;
    }
    qsort(str, count, 1, cmp_char);
    int num = 1;
    for (int i = 0; i < count - 1; i++) {
    
    
        if (str[i] != str[i + 1]) {
    
    
            num++;
        }
    }
    printf("%d", num);
    return 0;
}