题目：

题解：

class Solution {Map<Integer, Boolean> memo = new HashMap<Integer, Boolean>();public boolean canIWin(int maxChoosableInteger, int desiredTotal) {if ((1 + maxChoosableInteger) * (maxChoosableInteger) / 2 < desiredTotal) {return false;}return dfs(maxChoosableInteger, 0, desiredTotal, 0);}public boolean dfs(int maxChoosableInteger, int usedNumbers, int desiredTotal, int currentTotal) {if (!memo.containsKey(usedNumbers)) {boolean res = false;for (int i = 0; i < maxChoosableInteger; i++) {if (((usedNumbers >> i) & 1) == 0) {if (i + 1 + currentTotal >= desiredTotal) {res = true;break;}if (!dfs(maxChoosableInteger, usedNumbers | (1 << i), desiredTotal, currentTotal + i + 1)) {res = true;break;}}}memo.put(usedNumbers, res);}return memo.get(usedNumbers);}
}