Minimum Number of Flips to Have Alternating Values - Google Top Interview Questions


Problem Statement :


You are given a string s containing "1"s and "0"s. 

You can take some prefix of s and move it to the back. 

Afterwards, return the minimum number of characters that need to be flipped such that the string never has any two consecutive characters of the same value.

Constraints

n ≤ 100,000 where n is the length of s

Example 1

Input

s = "001010111"

Output

1

Explanation

After we move the first character "0" to the back we get "010101110". Then we can flip the 3rd last 
character to 0 and get "010101010".


Solution :



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                        Solution in C++ :

int solve(string s) {
    s += s;
    int n = s.size();
    vector<int> z(2), o(2);
    int ca = 0, ans = 1e6;
    for (int i = 0; i < n; i++) {
        if (s[i] == '1') {
            z[i % 2]++;
        } else {
            o[i % 2]++;
        }
        if (i >= n / 2) {
            int pr = i - n / 2;
            if (s[pr] == '1')
                z[pr % 2]--;
            else
                o[pr % 2]--;
            ca = min(z[0] + o[1], z[1] + o[0]);
            ans = min(ans, ca);
        }
    }
    return ans;
}
                    




                        Solution in Python : 
                            
class Solution:
    def solve(self, s):
        n = len(s)
        ret = n
        o = 0
        e = 0
        for i in range(2 * n):
            if (i % 2 == 0) == (s[i % n] == "0"):
                o += 1
            else:
                e += 1
            if i >= n:
                if ((i - n) % 2 == 0) == (s[i - n] == "0"):
                    o -= 1
                else:
                    e -= 1
            if i >= n - 1:
                ret = min(ret, min(o, e))
        return ret


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