py & cpp implementation

278. First Bad Version/main.cpp

@@ -0,0 +1,19 @@
+// Forward declaration of isBadVersion API.
+bool isBadVersion(int version);
+
+class Solution {
+public:
+  int firstBadVersion(int n) {
+    // 事实上，在最后一般需要判断。但这题确定target存在。
+    int left = 1, right = n, mid;
+    while (left < right) {
+      mid = (right - left) / 2 + left;
+      if (isBadVersion(mid)) {
+        right = mid;
+      } else {
+        left = mid + 1;
+      }
+    }
+    return left;
+  }
+};

278. First Bad Version/main.py

@@ -0,0 +1,23 @@
+# The isBadVersion API is already defined for you.
+# @param version, an integer
+# @return a bool
+# def isBadVersion(version):
+
+class Solution:
+    def firstBadVersion(self, n):
+        """
+        :type n: int
+        :rtype: int
+        """
+        left,right = 0,n
+        mid = 0
+        while left<right:
+            mid=(left+right)//2
+            if isBadVersion(mid):
+                right = mid
+            else:
+                left = mid + 1
+
+        # 事实上，在最后一般需要判断。但这题确定target存在。
+        return left
+