|
|
package class_2022_02_2_week;
|
|
|
|
|
|
// 测试链接 : https://leetcode.com/problems/24-game/
|
|
|
public class Code01_24Game {
|
|
|
|
|
|
public static boolean judgePoint24(int[] cards) {
|
|
|
if (cards == null || cards.length == 0) {
|
|
|
return false;
|
|
|
}
|
|
|
int n = cards.length;
|
|
|
Number[] arr = new Number[n];
|
|
|
for (int i = 0; i < n; i++) {
|
|
|
arr[i] = new Number(cards[i], 1);
|
|
|
}
|
|
|
return judge(arr, cards.length);
|
|
|
}
|
|
|
|
|
|
// arr中，有效的范围arr[0...size-1] ... 再往右，都无效了，不用看了！
|
|
|
public static boolean judge(Number[] arr, int size) {
|
|
|
if (size == 1) {
|
|
|
return arr[0].numerator == 24 && arr[0].denominator == 1;
|
|
|
}
|
|
|
for (int i = 0; i < size; i++) {
|
|
|
for (int j = i + 1; j < size; j++) {
|
|
|
Number inum = arr[i];
|
|
|
Number jnum = arr[j];
|
|
|
arr[j] = arr[size - 1];
|
|
|
arr[i] = add(inum, jnum);
|
|
|
if (judge(arr, size - 1)) {
|
|
|
return true;
|
|
|
}
|
|
|
arr[i] = minus(inum, jnum);
|
|
|
if (judge(arr, size - 1)) {
|
|
|
return true;
|
|
|
}
|
|
|
arr[i] = minus(jnum, inum);
|
|
|
if (judge(arr, size - 1)) {
|
|
|
return true;
|
|
|
}
|
|
|
arr[i] = multiply(inum, jnum);
|
|
|
if (judge(arr, size - 1)) {
|
|
|
return true;
|
|
|
}
|
|
|
arr[i] = divide(inum, jnum);
|
|
|
if (arr[i] != null && judge(arr, size - 1)) {
|
|
|
return true;
|
|
|
}
|
|
|
arr[i] = divide(jnum, inum);
|
|
|
if (arr[i] != null && judge(arr, size - 1)) {
|
|
|
return true;
|
|
|
}
|
|
|
arr[i] = inum;
|
|
|
arr[j] = jnum;
|
|
|
}
|
|
|
}
|
|
|
return false;
|
|
|
}
|
|
|
|
|
|
public static class Number {
|
|
|
public int numerator;
|
|
|
public int denominator;
|
|
|
|
|
|
public Number(int n, int d) {
|
|
|
numerator = n;
|
|
|
denominator = d;
|
|
|
}
|
|
|
}
|
|
|
|
|
|
public static Number add(Number a, Number b) {
|
|
|
return simple(a.numerator * b.denominator + b.numerator * a.denominator, a.denominator * b.denominator);
|
|
|
}
|
|
|
|
|
|
public static Number minus(Number a, Number b) {
|
|
|
return simple(a.numerator * b.denominator - b.numerator * a.denominator, a.denominator * b.denominator);
|
|
|
}
|
|
|
|
|
|
public static Number multiply(Number a, Number b) {
|
|
|
return simple(a.numerator * b.numerator, a.denominator * b.denominator);
|
|
|
}
|
|
|
|
|
|
public static Number divide(Number a, Number b) {
|
|
|
return b.numerator == 0 ? null : simple(a.numerator * b.denominator, a.denominator * b.numerator);
|
|
|
}
|
|
|
|
|
|
public static Number simple(int up, int down) {
|
|
|
if (up == 0) {
|
|
|
return new Number(0, 1);
|
|
|
}
|
|
|
int gcd = Math.abs(gcd(up, down));
|
|
|
return new Number(up / gcd, down / gcd);
|
|
|
}
|
|
|
|
|
|
public static int gcd(int a, int b) {
|
|
|
return b == 0 ? a : gcd(b, a % b);
|
|
|
}
|
|
|
|
|
|
}
|
