java

动态规划，分多情况讨论

import java.util.*;


public class Solution {
    public int solve (String nums) {
        // write code here
        if (nums == null || nums.length() == 0) {
            return 0;
        }
        if (nums.equals("0")) {
            return 0;
        }
        int[] dp = new int[nums.length()+1];
        dp[0] = 1;
        dp[1] = 1;
        for (int i = 2; i <= nums.length(); i++) {
            String str = nums.substring(i-2, i);
            if (str.charAt(1) == '0' && (str.charAt(0) > '2' || str.charAt(0) < '1')) {
                return 0;
            }else if (str.charAt(1) == '0' && (str.charAt(0) == '2' || str.charAt(0) == '1')) {
                dp[i] = dp[i-2];
            }else if (str.compareTo("01") >=0 && str.compareTo("09") <= 0){
                dp[i] = dp[i-1];
            }else if (str.compareTo("11") >= 0 && str.compareTo("26") <= 0) {
                dp[i] = dp[i - 1] + dp[i - 2];
            }else {
                dp[i] = dp[i-1];
            }
        }
        return dp[nums.length()];
    }
}