Include Solidity contract.

contracts/the-button.sol

@@ -0,0 +1,38 @@
+pragma solidity ^0.4.0;
+
+contract TheButton {
+    uint public timeLimit;
+    uint public lastPress;
+    mapping(address => uint) public pressTimes;
+
+    event ButtonPress(address pressedBy, uint time);
+
+    function TheButton(uint timeLimit_) public {
+        timeLimit = timeLimit_;
+        lastPress = now;
+    }
+
+    function press(uint expectLastPress) public returns (bool) {
+        // If the time limit expires, the game is over.
+        if (lastPress + timeLimit < now) {
+            return false;
+        }
+
+        // Don't allow users to press multiple times.
+        if (pressTimes[msg.sender] != 0) {
+            return false;
+        }
+
+        // Check the lastPress is the expected one so that if another user
+        // presses first, this one is rejected. The user should be notified
+        // that they should try again.
+        if (lastPress != expectLastPress) {
+            return false;
+        }
+
+        pressTimes[msg.sender] = now - lastPress;
+        lastPress = now;
+        ButtonPress(msg.sender, now);
+        return true;
+    }
+}