1017. Convert to Base -2

Given a number N, return a string consisting of "0"s and "1"s that represents its value in base -2 (negative two).

The returned string must have no leading zeroes, unless the string is "0".

 

Example 1:

Input: 2
Output: "110"
Explantion: (-2) ^ 2 + (-2) ^ 1 = 2

Example 2:

Input: 3
Output: "111"
Explantion: (-2) ^ 2 + (-2) ^ 1 + (-2) ^ 0 = 3

Example 3:

Input: 4
Output: "100"
Explantion: (-2) ^ 2 = 4

 

Note:

1. 0 <= N <= 10^9

 

Approach #1: Math. [Java]

class Solution {
    public String baseNeg2(int N) {
        if (N == 0) return "0";
        StringBuilder sb = new StringBuilder();
        while (N != 0) {
            int remainder = N % (-2);
            N /= -2;
            if (remainder < 0) {
                remainder += 2;
                N += 1;
            }
            sb.append(remainder);
        }
        return sb.reverse().toString();
    }
}

　　

<pre><code class="html">

#include<iostream>

#include<string>

#include<map>

#include<vector>

#include<set>

using namespace std;

int main() {

    string str;

    cin >> str;

    map<char, int> mp;

    for (int i = 0; i < str.length(); ++i) {

        mp[str[i]]++;

    }

    int start = 0, cur = 0, end;

    vector<int> ans;

    for (int i = 0; i < str.length(); ++i) {

        if (mp[str[cur]] == 0) {

            bool flag = false;

            for (int j = 1; j < i; ++j) {

                if (mp[str[j]] != 0) {

                    cur = j;

                    flag = true;

                    break;

                }

            }

            if (!flag) {

                ans.push_back(i-start);

                start = i;

                cur = start;

            }

        }

        mp[str[i]]--;

    }

    ans.push_back(str.length()-start);

    if (!ans.empty()) {

        cout << ans[0];

    }

    for (int i = 1; i < ans.size(); ++i)

        cout << " " << ans[i];

    return 0;

}

</code></pre>

 

Reference:

https://en.wikipedia.org/wiki/Negative_base#Calculation

https://www.geeksforgeeks.org/convert-number-negative-base-representation/