feat: add LeetCode problem 69

leetcode/src/69.c

@@ -0,0 +1,24 @@
+//using binary search method is one of the efficient one for this problem statement.
+int mySqrt(int x){
+int start=0;
+        int end=x;
+        long long int ans=0;
+        while(start <= end){
+               long long int mid=(start+end)/2;
+                long long int val=mid*mid;
+               if(mid*mid == x){
+                         return mid;
+                }
+//if mid is less than the square root of the number(x) store the value of mid in ans.
+               if( mid*mid < x){
+                         ans = mid;
+                       start = mid+1;
+               }
+//if mid is greater than the square root of the number(x) then ssign the value mid-1 to end.               
+               if( mid*mid > x){
+                       end = mid-1;
+               }
+        }
+        return ans;
+
+}