代码如下：
<script LANGUAGE="JavaScript"> <!-- Begin step = 0; diff=3; function clear_all(form) { step = 0; for (i=0;i<9; ++i) { position="a"+i; form[position].value=""; } } function clickit(field) { if (step == -1) {alert("重玩一局"); return;} position=field.name.substring(1,2,1); position = 'a'+position; if (field.form[position].value !="") {alert("不能这样走，有没搞错！"); return;} field.form[position].value="X"; if (eval_pos(field.form)) { field.form.output.value="你胜了!"; step = -1; return; } position=get_move(field.form); field.form.output.value='我下在' + position.substring(1,2,1)+'位'; if (position=="") { field.form.output.value="黄了"; step = -1; return; } field.form[position].value="O"; if (eval_pos(field.form)) { field.form.output.value="真没用，再来一局!"; step = -1; } } function eval_pos(form) { if ((form.a0.value!="" && form.a0.value==form.a3.value && form.a0.value==form.a6.value)|| (form.a0.value!="" && form.a0.value==form.a1.value && form.a0.value==form.a2.value) || (form.a0.value!="" && form.a0.value==form.a4.value && form.a0.value==form.a8.value) || (form.a1.value!="" && form.a1.value==form.a4.value && form.a1.value==form.a7.value) || (form.a2.value!="" && form.a2.value==form.a5.value && form.a2.value==form.a8.value) || (form.a2.value!="" && form.a2.value==form.a4.value && form.a2.value==form.a6.value) || (form.a3.value!="" && form.a3.value==form.a4.value && form.a3.value==form.a5.value) || (form.a6.value!="" && form.a6.value==form.a7.value && form.a6.value==form.a8.value)) return true; else return false; } function f(a) { if (a == "") return "."; else return a; } function comp_move(form,player,weight,depth) { var cost; var bestcost=-2; var position; var newplayer; if (player=="X") newplayer="O"; else newplayer="X"; if (depth==diff) return 0; if (eval_pos(form)) return 1; for (var i=0; i<9; ++i) { position='a'+i; if (form[position].value != "") continue; form[position].value=player; cost = comp_move(form,newplayer, -weight, depth+1); if (cost > bestcost) { bestcost=cost; if (cost==1) i=9; } form[position].value=""; } if (bestcost==-2) bestcost=0; return(-bestcost); } function get_move(form) { var cost; var bestcost=-2; bestmove=""; if (step++ == 0) if (form.a4.value=="") return "a4"; else if (form.a0.value=="") return "a0"; for (var i=0; i<9; ++i) { localposition='a'+i; if (form[localposition].value != "") continue; form[localposition].value="O"; cost=comp_move(form,"X", -1, 0); if (cost > bestcost) { if (cost==1) i=9; bestmove=localposition; bestcost=cost; } form[localposition].value=""; } return bestmove; } function complain(field) { field.form.output.focus(); alert("不能直接在输入框内按，要点按钮才行。"); } // End --> </script> <font color="red"> <form> <p><input SIZE="2" NAME="a0" OnFocus="complain(this)"> <input TYPE="button" NAME="b0" OnClick="clickit(this)"> <input SIZE="2" NAME="a1" OnFocus="complain(this)"> <input TYPE="button" NAME="b1" OnClick="clickit(this)"> <input SIZE="2" NAME="a2" OnFocus="complain(this)"> <input TYPE="button" NAME="b2" OnClick="clickit(this)"> <br> <input SIZE="2" NAME="a3" OnFocus="complain(this)"> <input TYPE="button" NAME="b3" OnClick="clickit(this)"> <input SIZE="2" NAME="a4" OnFocus="complain(this)"> <input TYPE="button" NAME="b4" OnClick="clickit(this)"> <input SIZE="2" NAME="a5" OnFocus="complain(this)"> <input TYPE="button" NAME="b5" OnClick="clickit(this)"> <br> <input SIZE="2" NAME="a6" OnFocus="complain(this)"> <input TYPE="button" NAME="b6" OnClick="clickit(this)"> <input SIZE="2" NAME="a7" OnFocus="complain(this)"> <input TYPE="button" NAME="b7" OnClick="clickit(this)"> <input SIZE="2" NAME="a8" OnFocus="complain(this)"> <input TYPE="button" NAME="b8" OnClick="clickit(this)"> <br> <br> 现场解说: <input NAME="output" TYPE="text" size="20"><br> 选择难度: <select NAME="difficulty" OnChange="diff=form.difficulty[form.difficulty.selectedIndex].value;" size="1"> <option VALUE="1"> 最简 </option> <option VALUE="2"> 容易 </option> <option VALUE="3" SELECTED> 中等 </option> <option VALUE="4"> 难 (可能时间要长些) </option> </select> <br> <input TYPE="button" VALUE="计算机先走" OnClick=" if (!step++) this.form.a4.value='O';"> <br> <input TYPE="reset" VALUE="重新再来" OnClick="clear_all(this.form)"> </p> </form> </body> </html>