add Solution 0069 [golang]

Author: lightfish-zhang

solution/0069.Sqrt(x)/Solution.go

@@ -0,0 +1,28 @@
+/**
+ * @lc app=leetcode.cn id=69 lang=golang
+ * Accepted
+ * 1017/1017 cases passed (0 ms)
+ * Your runtime beats 100 % of golang submissions
+ * Your memory usage beats 25.49 % of golang submissions (2.2 MB)
+ */
+
+func mySqrt(x int) int {
+	if x == 0 || x == 1 {
+		return x
+	}
+	l, r, t := 1, x, 0
+	m := (l + r) / 2
+	for l != m {
+		t = m * m
+		if t == x {
+			return m
+		}
+		if t < x {
+			l = m
+		} else {
+			r = m
+		}
+		m = (l + r) / 2
+	}
+	return m
+}