LeetCode #2457 — MEDIUM

Minimum Addition to Make Integer Beautiful

Move from brute-force thinking to an efficient approach using math strategy.

The Problem

Problem Statement

You are given two positive integers n and target.

An integer is considered beautiful if the sum of its digits is less than or equal to target.

Return the minimum non-negative integer x such that n + x is beautiful. The input will be generated such that it is always possible to make n beautiful.

Example 1:

Input: n = 16, target = 6
Output: 4
Explanation: Initially n is 16 and its digit sum is 1 + 6 = 7. After adding 4, n becomes 20 and digit sum becomes 2 + 0 = 2. It can be shown that we can not make n beautiful with adding non-negative integer less than 4.

Example 2:

Input: n = 467, target = 6
Output: 33
Explanation: Initially n is 467 and its digit sum is 4 + 6 + 7 = 17. After adding 33, n becomes 500 and digit sum becomes 5 + 0 + 0 = 5. It can be shown that we can not make n beautiful with adding non-negative integer less than 33.

Example 3:

Input: n = 1, target = 1
Output: 0
Explanation: Initially n is 1 and its digit sum is 1, which is already smaller than or equal to target.

Constraints:

1 <= n <= 10¹²
1 <= target <= 150
The input will be generated such that it is always possible to make n beautiful.

Step 01

Brute Force Baseline

Problem summary: You are given two positive integers n and target. An integer is considered beautiful if the sum of its digits is less than or equal to target. Return the minimum non-negative integer x such that n + x is beautiful. The input will be generated such that it is always possible to make n beautiful.

Baseline thinking

Start with the most direct exhaustive search. That gives a correctness anchor before optimizing.

Pattern signal: Math · Greedy

Example 1

16
6

Example 2

467
6

Example 3

1
1

Core Insight

What unlocks the optimal approach

Think about each digit independently.
Turn the rightmost non-zero digit to zero until the digit sum is greater than target.

Interview move: turn each hint into an invariant you can check after every iteration/recursion step.

Step 03

Algorithm Walkthrough

Iteration Checklist

Define state (indices, window, stack, map, DP cell, or recursion frame).
Apply one transition step and update the invariant.
Record answer candidate when condition is met.
Continue until all input is consumed.

Use the first example testcase as your mental trace to verify each transition.

Step 04

Edge Cases

Minimum Input

Single element / shortest valid input

Validate boundary behavior before entering the main loop or recursion.

Duplicates & Repeats

Repeated values / repeated states

Decide whether duplicates should be merged, skipped, or counted explicitly.

Extreme Constraints

Upper-end input sizes

Re-check complexity target against constraints to avoid time-limit issues.

Invalid / Corner Shape

Empty collections, zeros, or disconnected structures

Handle special-case structure before the core algorithm path.

Step 05

Full Annotated Code

Source-backed implementations are provided below for direct study and interview prep.

// Accepted solution for LeetCode #2457: Minimum Addition to Make Integer Beautiful
class Solution {
    public long makeIntegerBeautiful(long n, int target) {
        long x = 0;
        while (f(n + x) > target) {
            long y = n + x;
            long p = 10;
            while (y % 10 == 0) {
                y /= 10;
                p *= 10;
            }
            x = (y / 10 + 1) * p - n;
        }
        return x;
    }

    private int f(long x) {
        int y = 0;
        while (x > 0) {
            y += x % 10;
            x /= 10;
        }
        return y;
    }
}

// Accepted solution for LeetCode #2457: Minimum Addition to Make Integer Beautiful
func makeIntegerBeautiful(n int64, target int) (x int64) {
	f := func(x int64) (y int) {
		for ; x > 0; x /= 10 {
			y += int(x % 10)
		}
		return
	}
	for f(n+x) > target {
		y := n + x
		var p int64 = 10
		for y%10 == 0 {
			y /= 10
			p *= 10
		}
		x = (y/10+1)*p - n
	}
	return
}

# Accepted solution for LeetCode #2457: Minimum Addition to Make Integer Beautiful
class Solution:
    def makeIntegerBeautiful(self, n: int, target: int) -> int:
        def f(x: int) -> int:
            y = 0
            while x:
                y += x % 10
                x //= 10
            return y

        x = 0
        while f(n + x) > target:
            y = n + x
            p = 10
            while y % 10 == 0:
                y //= 10
                p *= 10
            x = (y // 10 + 1) * p - n
        return x

// Accepted solution for LeetCode #2457: Minimum Addition to Make Integer Beautiful
// Rust example auto-generated from java reference.
// Replace the signature and local types with the exact LeetCode harness for this problem.
impl Solution {
    pub fn rust_example() {
        // Port the logic from the reference block below.
    }
}

// Reference (java):
// // Accepted solution for LeetCode #2457: Minimum Addition to Make Integer Beautiful
// class Solution {
//     public long makeIntegerBeautiful(long n, int target) {
//         long x = 0;
//         while (f(n + x) > target) {
//             long y = n + x;
//             long p = 10;
//             while (y % 10 == 0) {
//                 y /= 10;
//                 p *= 10;
//             }
//             x = (y / 10 + 1) * p - n;
//         }
//         return x;
//     }
// 
//     private int f(long x) {
//         int y = 0;
//         while (x > 0) {
//             y += x % 10;
//             x /= 10;
//         }
//         return y;
//     }
// }

// Accepted solution for LeetCode #2457: Minimum Addition to Make Integer Beautiful
function makeIntegerBeautiful(n: number, target: number): number {
    const f = (x: number): number => {
        let y = 0;
        for (; x > 0; x = Math.floor(x / 10)) {
            y += x % 10;
        }
        return y;
    };

    let x = 0;
    while (f(n + x) > target) {
        let y = n + x;
        let p = 10;
        while (y % 10 === 0) {
            y = Math.floor(y / 10);
            p *= 10;
        }
        x = (Math.floor(y / 10) + 1) * p - n;
    }
    return x;
}

Step 06

Interactive Study Demo

Use this to step through a reusable interview workflow for this problem.

Custom checkpoints (one per line)

Press Step or Run All to begin.

Step 07

Complexity Analysis

Time

O(n log n)

Space

O(1)

Approach Breakdown

EXHAUSTIVE

O(2ⁿ) time

O(n) space

Try every possible combination of choices. With n items each having two states (include/exclude), the search space is 2ⁿ. Evaluating each combination takes O(n), giving O(n × 2ⁿ). The recursion stack or subset storage uses O(n) space.

GREEDY

O(n log n) time

O(1) space

Greedy algorithms typically sort the input (O(n log n)) then make a single pass (O(n)). The sort dominates. If the input is already sorted or the greedy choice can be computed without sorting, time drops to O(n). Proving greedy correctness (exchange argument) is harder than the implementation.

Shortcut: Sort + single pass → O(n log n). If no sort needed → O(n). The hard part is proving it works.

Coach Notes

Common Mistakes

Review these before coding to avoid predictable interview regressions.

Overflow in intermediate arithmetic

Wrong move: Temporary multiplications exceed integer bounds.

Usually fails on: Large inputs wrap around unexpectedly.

Fix: Use wider types, modular arithmetic, or rearranged operations.

Using greedy without proof

Wrong move: Locally optimal choices may fail globally.

Usually fails on: Counterexamples appear on crafted input orderings.

Fix: Verify with exchange argument or monotonic objective before committing.