DATA STRUCTURES PROGRAM • STACKS & EXPRESSIONS

Calculate Stock Span with a Monotonic Stack

Learn how to calculate stock span with a monotonic stack using a clear C program.

IntermediateStackLIFOpush/pop

PROBLEM UNDERSTANDING

Input and expected output

Sample input

No input required

Sample output

1 1 1 2 1 4 6

COMPLETE C PROGRAM

Complete C implementation

#include <stdio.h>

int main(void)
{
    int prices[] = {100, 80, 60, 70, 60, 75, 85};
    int stack[7], top = -1, spans[7];
    for (int day = 0; day < 7; day++) {
        while (top >= 0 && prices[stack[top]] <= prices[day]) top--;
        spans[day] = top < 0 ? day + 1 : day - stack[top];
        stack[++top] = day;
    }
    for (int day = 0; day < 7; day++) printf("%d ", spans[day]);
    putchar('\n');
    return 0;
}

CURRENT STEP

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SELECTED LINE

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EXPECTED OUTPUT FOR THE SAMPLE

1 1 1 2 1 4 6

0%Step 0 of 0

PROGRAM EXPLANATION

Algorithm and explanation

Read the required input values.
Store indices of previous greater prices and discard smaller prices permanently.
Display the computed result.

Store indices of previous greater prices and discard smaller prices permanently.

EFFICIENCY

Time and space complexity

Time complexity

O(n)

Auxiliary space

O(n)

DEBUGGING CHECKLIST

Common mistakes

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Use the correct format specifier for every variable.

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Initialize variables before using their values.

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Check braces, semicolons and input order carefully.

Try it yourself

Practice: Run the program with the sample input, predict its output, and then test one boundary case of your own.