编程练习（第十七周）

题目来源：https://leetcode.com

600. Non-negative Integers without Consecutive Ones

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• Total Accepted: 1587
• Total Submissions: 6069
• Difficulty: Hard
• Contributors:sanxi

Given a positive integer n, find the number of non-negative integers less than or equal to n, whose binary representations do NOT containconsecutive ones.

Example 1:

Input: 5Output: 5Explanation: Here are the non-negative integers <= 5 with their corresponding binary representations:0 : 01 : 12 : 103 : 114 : 1005 : 101Among them, only integer 3 disobeys the rule (two consecutive ones) and the other 5 satisfy the rule. 

Note: 1 <= n <= 109

代码如下：

int findIntegers(int num) {    string str="";    while(num>0)str+=num%2+'0',num/=2;    int l=str.length();    vector<int> arr(l+1,1);    for(int i=2;i<=l;i++)arr[i]=arr[i-1]+arr[i-2];    int result=1,pre=0;    for(int i=l;i>=0;i--)    {        if(str[i-1]=='1')        {            result+=arr[i];            if(pre==1)break;        }        pre=str[i-1]=='1';    }    return result-pre;}