finish 69

Author: BaffinLee

69. Sqrt(x).js

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+/**
+ * 69. Sqrt(x)
+ * 
+ * Implement int sqrt(int x).
+ * 
+ * Compute and return the square root of x, where x is guaranteed to be a non-negative integer.
+ * 
+ * Since the return type is an integer, the decimal digits are truncated and only the integer part of the result is returned.
+ * 
+ * Example 1:
+ * 
+ * Input: 4
+ * Output: 2
+ * 
+ * Example 2:
+ * 
+ * Input: 8
+ * Output: 2
+ * Explanation: The square root of 8 is 2.82842..., and since 
+ *              the decimal part is truncated, 2 is returned.
+ */
+
+/**
+ * @param {number} x
+ * @return {number}
+ */
+var mySqrt = function(x) {
+    if (x < 2) return x;
+    var left = 1;
+    var right = x;
+    var mid = 0;
+    while (left <= right) {
+        mid = left + Math.floor((right - left) / 2);
+        if (mid > x / mid) {
+            right = mid - 1;
+        } else if ((mid + 1) > x / (mid + 1)) {
+            return mid;
+        } else {
+            left = mid + 1;
+        }
+    }
+};