【剑指Offer】10.4 变态跳台阶

public int JumpFloorII(int target) {
    int[] dp = new int[target];
    Arrays.fill(dp, 1);
    for (int i = 1; i < target; i++)
        for (int j = 0; j < i; j++)
            dp[i] += dp[j];
    return dp[target - 1];
}

public class Solution {
  public int JumpFloorII(int target) {
    return target <= 0 ? 0 : 1 << (target - 1);
  }
}

public int JumpFloorII(int target) {
    return (int) Math.pow(2, target - 1);
}

int pow(int n) {
    int sum = 1;
    int tmp = 2;
    while(n != 0) {
        if(n & 1 == 1)
            sum *= tmp;
        
        temp *= temp;
        n >>= 1;
    }
    return sum;
}