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FlipGameII.java
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FlipGameII.java
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// 回溯
public boolean canWin(String s) {
if (s == null || s.length() < 2)
return false;
for (int i = 0; i < s.length() - 1; i++) {
if (s.startsWith("++", i)) {
String t = s.substring(0, i) + "--" + s.substring(i + 2);
if (!canWin(t)) return true;
}
}
return false;
}
// 搜索
public class Solution {
public boolean canWin(String s) {
boolean[] state = new boolean[s.length()];
for (int i = 0; i < s.length(); i++) {
if (s.charAt(i) == '+') {
state[i] = true;
} else {
state[i] = false;
}
}
return search(state);
}
public boolean search(boolean[] state) {
for (int i = 0; i < state.length - 1; i++) {
if (state[i] && state[i + 1]) {
state[i] = false;
state[i + 1] = false;
if (!search(state)) {
state[i] = true;
state[i + 1] = true;
return true;
} else {
state[i] = true;
state[i + 1] = true;
}
}
}
return false;
}
}
// 博弈
public class Solution {
public boolean canWin(String s) {
int[] nim = new int[s.length() + 1];
boolean[] happen = new boolean[s.length() + 1];
for (int i = 2; i <= s.length(); i++) {
for (int j = 0; j < i - j - 1; j++) {
happen[nim[j] ^ nim[i - j - 2]] = true;
}
boolean nimEmpty = true;
for (int j = 0; j <= s.length(); j++) {
if (!happen[j] && nimEmpty) {
nimEmpty = false;
nim[i] = j;
} else {
happen[j] = false;
}
}
}
int ans = 0;
int len = 0;
s = s + "-";
for (int i = 0; i < s.length(); i++) {
if (s.charAt(i) == '+') {
len++;
} else {
ans = ans ^ nim[len];
len = 0;
}
}
if (ans == 0) {
return false;
} else {
return true;
}
}
}