991. Broken Calculator

Problem

Tags: Math, Greedy

There is a broken calculator that has the integer startValue on its display initially. In one operation, you can:

• multiply the number on display by 2, or
• subtract 1 from the number on display.

Given two integers startValue and target, return the minimum number of operations needed to display target on the calculator.

Example 1:

Input: startValue = 2, target = 3
Output: 2
Explanation: Use double operation and then decrement operation {2 -> 4 -> 3}.

Example 2:

Input: startValue = 5, target = 8
Output: 2
Explanation: Use decrement and then double {5 -> 4 -> 8}.

Example 3:

Input: startValue = 3, target = 10
Output: 3
Explanation: Use double, decrement and double {3 -> 6 -> 5 -> 10}.

Constraints:

• 1 <= startValue, target <= 10^9

Code

C

// 991. Broken Calculator (11/30/54194)
// Runtime: 0 ms (94.96%) Memory: 5.38 MB (83.81%) 

int brokenCalc (int startValue, int target) {
    int operations = 0;
    
    while (startValue < target) {
        if (target % 2 == 0) {
            target >>= 1;
        } else {
            target++;
        }
        
        operations++;
    }
    
    return operations + (startValue - target);
}