755. Reach A Number¶

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755. Reach a Number

Medium

You are standing at position 0 on an infinite number line. There is a destination at position target.

You can make some number of moves numMoves so that:

• On each move, you can either go left or right.
• During the ith move (starting from i == 1 to i == numMoves), you take i steps in the chosen direction.

Given the integer target, return the minimum number of moves required (i.e., the minimum numMoves) to reach the destination.

Example 1:

Input: target = 2
Output: 3
Explanation:
On the 1st move, we step from 0 to 1 (1 step).
On the 2nd move, we step from 1 to -1 (2 steps).
On the 3rd move, we step from -1 to 2 (3 steps).

Example 2:

Input: target = 3
Output: 2
Explanation:
On the 1st move, we step from 0 to 1 (1 step).
On the 2nd move, we step from 1 to 3 (2 steps).

Constraints:

• -109 <= target <= 109
• target != 0

Solution¶

class Solution {
    public int reachNumber(int target) {
        if (target < 0) target = -1 * target;
        int res = 1, current_pos = 0;
        while (current_pos < target) current_pos += res++;
        while (((current_pos - target) & 1) > 0) current_pos += res++;
        return res - 1;
    }
}

Complexity Analysis¶

• Time Complexity: O(?)
• Space Complexity: O(?)

Approach¶

Detailed explanation of the approach will be added here