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464. Can I Win

Description

In the "100 game" two players take turns adding, to a running total, any integer from 1 to 10. The player who first causes the running total to reach or exceed 100 wins.

What if we change the game so that players cannot re-use integers?

For example, two players might take turns drawing from a common pool of numbers from 1 to 15 without replacement until they reach a total >= 100.

Given two integers maxChoosableInteger and desiredTotal, return true if the first player to move can force a win, otherwise, return false. Assume both players play optimally.

 

Example 1:

Input: maxChoosableInteger = 10, desiredTotal = 11
Output: false
Explanation:
No matter which integer the first player choose, the first player will lose.
The first player can choose an integer from 1 up to 10.
If the first player choose 1, the second player can only choose integers from 2 up to 10.
The second player will win by choosing 10 and get a total = 11, which is >= desiredTotal.
Same with other integers chosen by the first player, the second player will always win.

Example 2:

Input: maxChoosableInteger = 10, desiredTotal = 0
Output: true

Example 3:

Input: maxChoosableInteger = 10, desiredTotal = 1
Output: true

 

Constraints:

  • 1 <= maxChoosableInteger <= 20
  • 0 <= desiredTotal <= 300

Solutions

  • class Solution {
        private Map<Integer, Boolean> memo = new HashMap<>();
    
        public boolean canIWin(int maxChoosableInteger, int desiredTotal) {
            int s = (1 + maxChoosableInteger) * maxChoosableInteger / 2;
            if (s < desiredTotal) {
                return false;
            }
            return dfs(0, 0, maxChoosableInteger, desiredTotal);
        }
    
        private boolean dfs(int state, int t, int maxChoosableInteger, int desiredTotal) {
            if (memo.containsKey(state)) {
                return memo.get(state);
            }
            boolean res = false;
            for (int i = 1; i <= maxChoosableInteger; ++i) {
                if (((state >> i) & 1) == 0) {
                    if (t + i >= desiredTotal
                        || !dfs(state | 1 << i, t + i, maxChoosableInteger, desiredTotal)) {
                        res = true;
                        break;
                    }
                }
            }
            memo.put(state, res);
            return res;
        }
    }
    
  • class Solution {
    public:
        bool canIWin(int maxChoosableInteger, int desiredTotal) {
            int s = (1 + maxChoosableInteger) * maxChoosableInteger / 2;
            if (s < desiredTotal) return false;
            unordered_map<int, bool> memo;
            return dfs(0, 0, maxChoosableInteger, desiredTotal, memo);
        }
    
        bool dfs(int state, int t, int maxChoosableInteger, int desiredTotal, unordered_map<int, bool>& memo) {
            if (memo.count(state)) return memo[state];
            bool res = false;
            for (int i = 1; i <= maxChoosableInteger; ++i) {
                if ((state >> i) & 1) continue;
                if (t + i >= desiredTotal || !dfs(state | 1 << i, t + i, maxChoosableInteger, desiredTotal, memo)) {
                    res = true;
                    break;
                }
            }
            memo[state] = res;
            return res;
        }
    };
    
  • class Solution:
        def canIWin(self, maxChoosableInteger: int, desiredTotal: int) -> bool:
            @cache
            def dfs(state, t):
                for i in range(1, maxChoosableInteger + 1):
                    if (state >> i) & 1:
                        continue
                    if t + i >= desiredTotal or not dfs(state | 1 << i, t + i):
                        return True
                return False
    
            s = (1 + maxChoosableInteger) * maxChoosableInteger // 2
            if s < desiredTotal:
                return False
            return dfs(0, 0)
    
    
  • func canIWin(maxChoosableInteger int, desiredTotal int) bool {
    	s := (1 + maxChoosableInteger) * maxChoosableInteger / 2
    	if s < desiredTotal {
    		return false
    	}
    	memo := map[int]bool{}
    	var dfs func(int, int) bool
    	dfs = func(state, t int) bool {
    		if v, ok := memo[state]; ok {
    			return v
    		}
    		res := false
    		for i := 1; i <= maxChoosableInteger; i++ {
    			if (state>>i)&1 == 1 {
    				continue
    			}
    			if t+i >= desiredTotal || !dfs(state|1<<i, t+i) {
    				res = true
    				break
    			}
    		}
    		memo[state] = res
    		return res
    	}
    	return dfs(0, 0)
    }
    

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