69-Sqrt(x)

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题意

Given a non-negative integer x, compute and return the square root of x. 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: x = 4
Output: 2

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

思路

• 数学题: 二分法
• 调库

class Solution(object):
    def mySqrt(self, x):
        """
        :type x: int
        :rtype: int
        """
        '''
        1, 2, 3, 4, 5, 6, 7, 8
        low      mid         high
        low   high
           mid
              low
           high
        '''
        if x == 0: return 0
        low, high = 1, x
        while low <= high:
            mid = (high - low) /2  + low
            if mid * mid == x: return mid
            elif mid * mid < x: low = mid + 1
            else: high = mid - 1
        
        # 找不到target: high < target < low
        return high
        
    def mySqrt2(self, x):
        """
        :type x: int
        :rtype: int
        """
        return int(x**0.5)

分析:

• Time: O(logn)
• Space: O(1)