A number is a gapful number when −
- It has at least three digits, and
- It is exactly divisible by the number formed by putting its first and last digits together
For example −
The number 1053 is a gapful number because it has 4 digits and it is exactly divisible by 13. Similarly, 135 is a gapful number because it has 3 digits and it is exactly divisible by 15.
Our job is to write a program that returns the nearest gapful number to the number we provide as input.
For example, for all 2-digit numbers, it would be 100. For 103, it would be 105.
We will break the problem into two functions −
isGapful() function
It receives a number string and returns a boolean as in the below code −
const isGapful = (numStr) => { const int = parseInt(numStr); return int % parseInt(numStr[0] + numStr[numStr.length - 1]) === 0; };
nearestGapful() function
This is our main function that receives a number, returns the nearest gapful number. Here’s the code −
const nearestGapful = (num) => { if(typeof num !== 'number'){ return -1; } if(num <= 100){ return 100; } let prev = num - 1, next = num + 1; while(!isGapful(String(prev)) && !isGapful(String(next))){ prev--; next++; }; return isGapful(String(prev)) ? prev : next; };
The isGapful() function returns a boolean based on whether the number is gapful or not in constant time, the nearestGapful() function loops until it finds a number that is gapful and returns it.
Following is the complete code −
Example
const n = 134; //receives a number string and returns a boolean const isGapful = (numStr) => { const int = parseInt(numStr); return int % parseInt(numStr[0] + numStr[numStr.length - 1]) === 0; }; //main function -- receives a number, returns a number const nearestGapful = (num) => { if(typeof num !== 'number'){ return -1; } if(num <= 100){ return 100; } let prev = num - 1, next = num + 1; while(!isGapful(String(prev)) && !isGapful(String(next))){ prev--; next++; }; return isGapful(String(prev)) ? prev : next; }; console.log(nearestGapful(n));
Output
The output in the console will be −
135