6 zigzag
1 sort by rows
class Solution {
public String convert(String s, int numRows) {
if (numRows == 1) return s;
List<StringBuilder> rows = new ArrayList<>();
for (int i=0; i < numRows; i++) rows.add(new StringBuilder());
int curRows = 0;
boolean goingDown = false;
for (char c: s.toCharArray()) {
rows.get(curRows).append(c);
if (curRows == 0 || curRows == numRows - 1) goingDown = !goingDown;
curRows += (goingDown) ? 1:-1;
}
StringBuilder rec = new StringBuilder();
for (StringBuilder row : rows)
rec.append(row);
return rec.toString();
}
}
- 反转
注意上下逸出
class Solution {
public int reverse(int x) {
int rev = 0;
while (x != 0) {
int pop = x % 10;
x /= 10;
if (rev > Integer.MAX_VALUE/10 ) return 0;
if (rev < Integer.MIN_VALUE/10 ) return 0;
rev = rev * 10 + pop;
}
return rev;
}
}
