679. 24 点游戏

src/main.rs

@@ -1,29 +1,106 @@
+enum Operation {
+    Add,
+    Subtract,
+    Multiply,
+    Divide,
+}
+enum Card {
+    Int(i32),
+    Op(Operation),
+}
 struct Solution;
 impl Solution {
-    // return type: all situation, not crash situation
-    pub fn new21_game(n: i32, k: i32, max_pts: i32) -> f64 {
-        let mut mem = vec![0f64; (k + max_pts + 1) as usize];
-        for i in k .. k + max_pts + 1 {
-            mem[i as usize] = if i <= n { 1f64 } else { 0f64 };
-        }
-        let mut temp_ans = 0f64;
-        if(k - 1 >= 0)
-        {
-            let i = k - 1;
-            for j in 1..max_pts + 1 {
-                temp_ans += mem[(i + j) as usize];
+    fn solve(cards: &Vec<Card>) -> bool {
+        let mut stack = Vec::new();
+        for t in cards.iter() {
+            if let Card::Op(op) = t {
+                if stack.len() < 2 {
+                    return false;
+                }
+                let b = stack.pop().unwrap() as f64;
+                let a = stack.pop().unwrap() as f64;
+                let result = match op {
+                    Operation::Add => a + b,
+                    Operation::Subtract => a - b,
+                    Operation::Multiply => a * b,
+                    Operation::Divide => {
+                        if b == 0f64 {
+                            return false;
+                        }
+                        a / b
+                    }
+                };
+                stack.push(result);
+            } else if let Card::Int(num) = t {
+                stack.push(*num as f64);
             }
-            mem[i as usize] = temp_ans as f64 / max_pts as f64;
         }
-        for i in (0..k - 1).rev() {
-            temp_ans += mem[(i + 1) as usize] - mem[(i + max_pts + 1) as usize];
-            mem[i as usize] = temp_ans as f64 / max_pts as f64;
+        if stack.len() != 1 {
+            return false;
         }
-        mem[0]
+        (24f64 - stack[0]).abs() < 1e-5
+    }
+    fn dfs(cards: &Vec<i32>, card_objects: &mut Vec<Card>, visited: &mut Vec<bool>) -> bool {
+        if card_objects.len() == 7 {
+            return Self::solve(card_objects);
+        }
+        for i in 0..8 {
+            if i <= 3 {
+                if visited[i] {
+                    continue;
+                }
+                visited[i] = true;
+                card_objects.push(Card::Int(cards[i]));
+                if Self::dfs(cards, card_objects, visited) {
+                    return true;
+                }
+                card_objects.pop();
+                visited[i] = false;
+            }
+            else {
+                let op = match i {
+                    4 => Operation::Add,
+                    5 => Operation::Subtract,
+                    6 => Operation::Multiply,
+                    _ => Operation::Divide,
+                };
+                card_objects.push(Card::Op(op));
+                if Self::dfs(cards, card_objects, visited) {
+                    return true;
+                }
+                card_objects.pop();
+            }
+        }
+        false
+    }
+
+    pub fn judge_point24(cards: Vec<i32>) -> bool {
+        let mut visited = vec![false; 4];
+        let mut card_objects = Vec::new();
+        for i in 0..4 {
+            visited[i] = true;
+            card_objects.push(Card::Int(cards[i]));
+            for j in 0..4 {
+                if visited[j] {
+                    continue;
+                } else {
+                    visited[j] = true;
+                    card_objects.push(Card::Int(cards[j]));
+                    if Self::dfs(&cards, &mut card_objects, &mut visited) {
+                        return true;
+                    }
+                    card_objects.pop();
+                    visited[j] = false;
+                }
+            }
+            card_objects.pop();
+            visited[i] = false;
+        }
+        false
     }
 }
 
 fn main() {
-    let sl = Solution::new21_game(21, 17, 10);
+    let sl = Solution::judge_point24(vec![3,3,8,8]);
     println!("{:?}", sl);
 }