LeetCode 69. Sqrt(x) (Java)

Description

https://leetcode.com/problems/sqrtx/description/

Implement int sqrt(int x).

Compute and return the square root of x.

x is guaranteed to be a non-negative integer.

Example 1:

Input: 4
Output: 2

Example 2:

Input: 8
Output: 2
Explanation: The square root of 8 is 2.82842..., and since we want to return an integer, the decimal part will be truncated.

Explanation

We can convert square root from a math problem to a computer science problem. To find a square root is actually to search for a number among 0 to x. Just use binary search to solve the problem.

Video Tutorial

Java Solution

class Solution {
    public int mySqrt(int x) {
        long start = 0;
        long end = x;
        
        while (start + 1 < end) {
            long mid = start + (end - start) / 2;
            if (mid * mid == x) {
                return (int)mid;
            } else if (mid * mid < x) {
                start = mid;
            } else {
                end = mid;
            }
        }
        
        if (end * end == x) {
            return (int)end;
        }
        return (int)start;
    }
}

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