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Code01_Light.java
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105 lines (97 loc) · 2.6 KB
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package class14;
import java.util.HashSet;
public class Code01_Light {
public static int minLight1(String road) {
if (road == null || road.length() == 0) {
return 0;
}
return process(road.toCharArray(), 0, new HashSet<>());
}
// str[index....]位置，自由选择放灯还是不放灯
// str[0..index-1]位置呢？已经做完决定了，那些放了灯的位置，存在lights里
// 要求选出能照亮所有.的方案，并且在这些有效的方案中，返回最少需要几个灯
public static int process(char[] str, int index, HashSet<Integer> lights) {
if (index == str.length) { // 结束的时候
for (int i = 0; i < str.length; i++) {
if (str[i] != 'X') { // 当前位置是点的话
if (!lights.contains(i - 1) && !lights.contains(i) && !lights.contains(i + 1)) {
return Integer.MAX_VALUE;
}
}
}
return lights.size();
} else { // str还没结束
// i X .
int no = process(str, index + 1, lights);
int yes = Integer.MAX_VALUE;
if (str[index] == '.') {
lights.add(index);
yes = process(str, index + 1, lights);
lights.remove(index);
}
return Math.min(no, yes);
}
}
public static int minLight2(String road) {
char[] str = road.toCharArray();
int i = 0;
int light = 0;
while (i < str.length) {
if (str[i] == 'X') {
i++;
} else {
light++;
if (i + 1 == str.length) {
break;
} else { // 有i位置 i+ 1 X .
if (str[i + 1] == 'X') {
i = i + 2;
} else {
i = i + 3;
}
}
}
}
return light;
}
// 更简洁的解法
// 两个X之间，数一下.的数量，然后除以3，向上取整
// 把灯数累加
public static int minLight3(String road) {
char[] str = road.toCharArray();
int cur = 0;
int light = 0;
for (char c : str) {
if (c == 'X') {
light += (cur + 2) / 3;
cur = 0;
} else {
cur++;
}
}
light += (cur + 2) / 3;
return light;
}
// for test
public static String randomString(int len) {
char[] res = new char[(int) (Math.random() * len) + 1];
for (int i = 0; i < res.length; i++) {
res[i] = Math.random() < 0.5 ? 'X' : '.';
}
return String.valueOf(res);
}
public static void main(String[] args) {
int len = 20;
int testTime = 100000;
for (int i = 0; i < testTime; i++) {
String test = randomString(len);
int ans1 = minLight1(test);
int ans2 = minLight2(test);
int ans3 = minLight3(test);
if (ans1 != ans2 || ans1 != ans3) {
System.out.println("oops!");
}
}
System.out.println("finish!");
}
}