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Code02_EatGrass.java
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Code02_EatGrass.java
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package class38;
public class Code02_EatGrass {
// 如果n份草,最终先手赢,返回"先手"
// 如果n份草,最终后手赢,返回"后手"
public static String whoWin(int n) {
if (n < 5) {
return n == 0 || n == 2 ? "后手" : "先手";
}
// 进到这个过程里来,当前的先手,先选
int want = 1;
while (want <= n) {
if (whoWin(n - want).equals("后手")) {
return "先手";
}
if (want <= (n / 4)) {
want *= 4;
} else {
break;
}
}
return "后手";
}
public static String winner1(int n) {
if (n < 5) {
return (n == 0 || n == 2) ? "后手" : "先手";
}
int base = 1;
while (base <= n) {
if (winner1(n - base).equals("后手")) {
return "先手";
}
if (base > n / 4) { // 防止base*4之后溢出
break;
}
base *= 4;
}
return "后手";
}
public static String winner2(int n) {
if (n % 5 == 0 || n % 5 == 2) {
return "后手";
} else {
return "先手";
}
}
public static void main(String[] args) {
for (int i = 0; i <= 50; i++) {
System.out.println(i + " : " + whoWin(i));
}
}
}