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LeetCode1545.java

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package problems;

public class LeetCode1545 {

public char findKthBit(int n, int k) {

String str = "0";

// String str = "";

for (int i = 2; i <= n; i++) {

str = str + "1" + reverse(invert(str));

}

return str.charAt(k-1);

}

private String invert(String str){

StringBuilder builder = new StringBuilder();

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

if(str.charAt(i) == '0'){

builder.append('1');

}else{

builder.append('0');

}

}

return builder.toString();

}

private String reverse(String str){

StringBuilder builder = new StringBuilder(str);

return builder.reverse().toString();

}

public static void main(String[] args) {

LeetCode1545 leetCode1545 = new LeetCode1545();

leetCode1545.findKthBit(4, 11);

}

}

class LeetCode1545_1{

public char findKthBit(int n, int k) {

if (k == 1) {

return '0';

}

int mid = 1 << (n - 1);

if (k == mid) {

return '1';

} else if (k < mid) {

return findKthBit(n - 1, k);

} else {

k = mid * 2 - k;

return invert(findKthBit(n - 1, k));

}

}

public char invert(char bit) {

return (char) ('0' + '1' - bit);

}

}