surtax.py

Author: Chris Wu

problems/sqrtx.py

@@ -0,0 +1,27 @@
+"""
+The ans must be in between 0 and `x`.
+So we set the lower bound `l` to 0. The upper bound `r` to `x`.
+The answer will always between `l` and `r`.
+For every iteration, if `l`, `m`, `r` are not answer, we adjust the `l` or `r`.
+Until we find the answer
+"""
+class Solution(object):
+    def mySqrt(self, x):
+        def isAns(a):
+            if a**2<=x and (a+1)**2>x:
+                return True
+            return False
+
+        l = 0
+        r = x
+        while True:
+            m = (l+r)/2
+            if isAns(l): return l
+            if isAns(m): return m
+            if isAns(r): return r
+
+            if m**2<x:
+                l = m+1
+            else:
+                r = m-1
+        return -1