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I have 2 arrays: int element[3] = {0, 1, 2}; int quantity[3] = {2, 3, 4}; Now I want a result array that will have two zeros, three ones and four twos. int result[2+3+4] = {0, 0, 1, 1, 1, 2, 2, 2, 2}; How do I do this using loop?

Vlad from Moscow
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Min Bani Adam
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  • A good start would be to calculate the size of the new `result` array. Then perhaps a loop over the `element` array. And inside that loop, a loop using the corresponding value from `quantity`. – Some programmer dude Oct 26 '22 at 09:00
  • "... and a partridge in a pear tree..." `:-)` ... Seriously, `realloc()` could be used to achieve this with a single loop growing the array (and a trivial inner loop poking repetitions of a value into its elements.) Hint: `realloc( NULL, n );` acts just like `malloc( n )`... Start with 0 and work your way up to the completed array. – Fe2O3 Oct 26 '22 at 09:13
  • @Jabberwocky You have the elements and their quantity. Now produce the resulting array. – Min Bani Adam Oct 26 '22 at 09:20

2 Answers2

1

You need to count the number of elements in the result array and to declare either a variable length array with the calculated value or to allocate dynamically such an array.

For example

int quantity[3] = {2, 3, 4};

size_t n = 0;
for ( size_t i = 0; i < 3; i++ )
{
    n += quantity[i];
}

int result[n];

// or
// int *result = malloc( n * sizeof( int ) );

And then in nested loops you need fill the resulted array.

For example

for ( size_t i = 0, j = 0; i < 3; i++ )
{
    for ( size_t k = 0; k < quantity[i]; k++ )
    {
        result[j++] = element[i];
    }
}
Vlad from Moscow
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1

Firstly we need to calculate the size of the result array. Then start populating your result array each element at a time. While we populate the result array, we need to increment the index.

int elementSize = sizeof(element)/sizeof(element[0]);
int resultSize = 0;

//pre calculating the size of result array
for(int i=0;i<elementSize;i++ ) {
    resultSize += quantity[i];
}

int result[resultSize], currIndex = 0;
//picking each element
for(int i = 0;i< elementSize; i++ ) {
    int currElement = element[i];
    int currQuantity = quantity[i];

//filling the current element required no of times in the result array
    while(currQuantity--) {
        result[currIndex] = currElement;
        currIndex++;
    }
}

//just a for loop to check the elements inside result array
for(int i=0;i<resultSize;i++)
    printf("%d\n",result[i]);
deathByChocolate
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