2022-06-18

6. Zigzag Conversion

Description

The string `"PAYPALISHIRING"` is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility)

``````P   A   H   N
A P L S I I G
Y   I   R``````

And then read line by line: `"PAHNAPLSIIGYIR"`

Write the code that will take a string and make this conversion given a number of rows:

``string convert(string s, int numRows);``

Example 1:

``````Input: s = "PAYPALISHIRING", numRows = 3
Output: "PAHNAPLSIIGYIR"``````

Example 2:

``````Input: s = "PAYPALISHIRING", numRows = 4
Output: "PINALSIGYAHRPI"
Explanation:
P     I    N
A   L S  I G
Y A   H R
P     I``````

Example 3:

``````Input: s = "A", numRows = 1
Output: "A"``````

Constraints:

• `1 <= s.length <= 1000`

• `s` consists of English letters (lower-case and upper-case), `','` and `'.'`.

• `1 <= numRows <= 1000`

Solution

Approach #0

``````func convert(s string, numRows int) string {
n, r := len(s), numRows
if r == 1 || n <= r {
return s
}
t := 2*r - 2
c := int(math.Ceil(float64(n)/float64(t))) * (r - 1)
mat := make([][]byte, r)
for i := 0; i < r; i++ {
mat[i] = make([]byte, c)
}
x, y := 0, 0
for i, ch := range s {
mat[x][y] = byte(ch)
if i%t < r-1 {
x++
} else {
x--
y++
}
}
var ans []byte
for i := 0; i < r; i++ {
for j := 0; j < c; j++ {
if mat[i][j] > 0 {
ans = append(ans, mat[i][j])
}
}
}
return string(ans)
}``````

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