Leetcode 69. Sqrt(x)

Implement int sqrt(int x).

Compute and return the square root of x, where x is guaranteed to be a non-negative integer.

Since the return type is an integer, the decimal digits are truncated and only the integer part of the result is returned.

Example 1:

Input: 4 Output: 2

Example 2:

Input: 8 Output: 2 Explanation: The square root of 8 is 2.82842..., and since the decimal part is truncated, 2 is returned.

Difficulty:Easy

Category:Math, Binary-Search

Analyze

Solution

Solution 1: Binary Search

Time Complexity: O(log n), Space Complexity: O(1)

class Solution {
public:
  int mySqrt(int x) {
    if (x < 2) return x;
    int left = 0, right = x / 2 + 1;
    while (left < right) {
      int mid = left + (right - left) / 2;
      // Move left == right, then we need to move left back
      x / mid < mid ? right = mid : left = mid + 1;
    }

    return left - 1;
  }
};