1758. Minimum Changes To Make Alternating Binary String

#### QUESTION:

You are given a string s consisting only of the characters ‘0’ and ‘1’. In one operation, you can change any ‘0’ to ‘1’ or vice versa.

The string is called alternating if no two adjacent characters are equal. For example, the string “010” is alternating, while the string “0100” is not.

Return the minimum number of operations needed to make s alternating.

Example 1:

``````Input: s = "0100"
Output: 1
Explanation: If you change the last character to '1', s will be "0101", which is alternating.
``````

Example 2:

``````Input: s = "10"
Output: 0
``````

Example 3:

``````Input: s = "1111"
Output: 2
Explanation: You need two operations to reach "0101" or "1010".
``````

Constraints:

``````1 <= s.length <= 104
s[i] is either '0' or '1'.
``````

#### SOLUTION:

``````class Solution {
func minOperations(_ s: String) -> Int {
var tmp0 = true
var tmp1 = true
var result0 = 0
var result1 = 0
for ch in s {
if (tmp0) { // 当前位置应该为0
if (ch == "0") {

} else {
result0 += 1
}
} else {
if (ch == "0") {
result0 += 1
} else {

}
}
if (tmp1) { // 当前位置应该为1
if (ch == "1") {

} else {
result1 += 1
}
} else {
if (ch == "1") {
result1 += 1
} else {

}
}
tmp0 = !tmp0
tmp1 = !tmp1
}
return min(result0, result1)
}
}
``````