Create 69. Sqrt(x)

Author: rongweihe

69. Sqrt(x)

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+[https://leetcode.com/problems/sqrtx/description/]
+Implement int sqrt(int x).
+
+Compute and return the square root of x.
+``` c++
+class Solution {
+public:
+    int mySqrt(int x) {
+       // long long xx=x;
+        long long left=0;
+        long long right=x/2+1;
+        while(left<=right)
+        {
+            long long mid=(left+right)/2;
+            long long sq=mid*mid;
+            if(sq==x) return mid;
+            else if(sq<x) left=mid+1;
+            else right=mid-1;
+        }
+        return right;
+    }
+};
+```