class Solution {
    public int climbStairs(int n) {
        int dp[] = new int[n+1];
        if(n <= 2) return n;
        dp[1] = 1;
        dp[2] = 2;
        for(int i = 3;i <= n;i++){
            dp[i] = dp[i-1] + dp[i-2];
        }
        return dp[n];
    }
}

class Solution {
    public int climbStairs(int n) {
        int dp[] = new int[4];
        if(n <= 2) return n;
        dp[1] = 1;
        dp[2] = 2;
        for(int i = 3;i <= n;i++){
            dp[3] = dp[1] + dp[2];
            dp[1] = dp[2];
            dp[2] = dp[3];
        }
        return dp[3];
    }
}

class Solution {
    public int maxProfit(int[] prices) {
        int res = 0;
        int min = Integer.MAX_VALUE;
        for(int i = 0;i < prices.length;i++){
            res = Math.max(res,prices[i]-min);
            min = Math.min(min,prices[i]);
        }
        return res;
    }
}

class Solution {
    public boolean isMatch(String s, String p) {
        int m = s.length();
        int n = p.length();
        boolean[][] f = new boolean[m + 1][n + 1];
        f[0][0] = true;
        for (int i = 0; i <= m; ++i) {
            for (int j = 1; j <= n; ++j) {
                if (p.charAt(j - 1) == '*') {
                    f[i][j] = f[i][j - 2];
                    if (matches(s, p, i, j - 1)) {
                        f[i][j] = f[i][j] || f[i - 1][j];
                    }
                } else {
                    if (matches(s, p, i, j)) {
                        f[i][j] = f[i - 1][j - 1];
                    }
                }
            }
        }
        return f[m][n];
    }
    public boolean matches(String s, String p, int i, int j) {
        if (i == 0) {
            return false;
        }
        if (p.charAt(j - 1) == '.') {
            return true;
        }
        return s.charAt(i - 1) == p.charAt(j - 1);
    }
}