【leetcode】306（Medium）Additive Number

解题思路

不断截取字符串来验证

提交代码

class Solution {
    public boolean isAdditiveNumber(String num) {
    	if(num==null||num.length()<3)	return false;
    	if(num.equals("000"))	return true;
    	int len=num.length();
		for(int p1=1;p1<=len/2+1;p1++) {
			for(int p2=p1+1;p2<=len/2+2;p2++) {
				if(p2==num.length())	return false;
				int num1=getNum(num.substring(0,p1));
				int num2=getNum(num.substring(p1, p2));
				if((num.charAt(0)=='0'&&num1!=0)||(num.charAt(p1)=='0'&&num2!=0))
					continue;
				int range=Math.max(p1, p2-p1);
				if(helper(num1,num2,range,num.substring(p2)))	return true;
			}
		}
    	return false;
    }
    
    private boolean helper(int num1,int num2,int range,String s) {
    	if(s.equals(""))	return true;
    	else if(s.charAt(0)=='0'||s.length()<range)	return false;
    	
    	int num3=getNum(s.substring(0,range));
    	if(num1+num2==num3)
    		if(helper(num2,num3,range,s.substring(range)))	return true;
    	if(range+1<=s.length()) {
    	num3=getNum(s.substring(0,range+1));
    	if(num1+num2==num3)
    		if(helper(num2,num3,range+1,s.substring(range+1)))	return true;
    	}
    	return false;
    }
    
    
    private int getNum(String s) {
    	int res=0;
    	for(int i=0;i<s.length();i++) {
    		res*=10;
    		res+=s.charAt(i)-'0';
    	}
    	return res;
    }
}

运行结果