633. Sum of Square Numbers

Medium
Given a non-negative integer c, decide whether there're two integers a and b such that a2 + b2 = c.
Example 1:
Input: c = 5
Output:
true
Explanation:
1 * 1 + 2 * 2 = 5
Example 2:
Input: c = 3
Output:
false
Constraints:
  • 0 <= c <= 231 - 1

解題

Binary search 來解題,最右邊的值設定為 c 開根號。
Runtime: 0 ms, faster than 100%
Memory Usage: 1.9 MB, less than 34.88%
func judgeSquareSum(c int) bool {
if c == 1 { return true }
left := 0
right := int(math.Sqrt(float64(c)))
​
for left <= right {
sum := left * left + right * right
​
if sum == c {
return true
} else if sum > c {
right--
} else {
left++
}
}
​
return false
}