Valid Word Square

题目地址：
https://leetcode.com/problems/valid-word-square/description/

题目：

Given a sequence of words, check whether it forms a valid word square.

A sequence of words forms a valid word square if the kth row and column read the exact same string, where 0 ≤ k < max(numRows, numColumns).

Note:

1. The number of words given is at least 1 and does not exceed 500.
2. Word length will be at least 1 and does not exceed 500.
3. Each word contains only lowercase English alphabet a-z.

Example 1:

Input:
[
  "abcd",
  "bnrt",
  "crmy",
  "dtye"
]

Output:
true

Explanation:
The first row and first column both read "abcd".
The second row and second column both read "bnrt".
The third row and third column both read "crmy".
The fourth row and fourth column both read "dtye".

Therefore, it is a valid word square.

Example 2:

Input:
[
  "abcd",
  "bnrt",
  "crm",
  "dt"
]

Output:
true

Explanation:
The first row and first column both read "abcd".
The second row and second column both read "bnrt".
The third row and third column both read "crm".
The fourth row and fourth column both read "dt".

Therefore, it is a valid word square.

Example 3:

Input:
[
  "ball",
  "area",
  "read",
  "lady"
]

Output:
false

Explanation:
The third row reads "read" while the third column reads "lead".

Therefore, it is NOT a valid word square.

解题思路：
这道题就是将输入转化成char的matrix就可以了

代码：

public boolean validWordSquare(List<String> words) {
    if(words == null || words.size() == 0){
        return true;
    }
    int row = words.size();
    int maxRowLen = 0;
    for(int i = 0; i <= row - 1; i++){
        maxRowLen = Math.max(words.get(i).length(), maxRowLen);
    }
    int size = Math.max(row, maxRowLen);
    char[][] matrix = convert(words, size);
    for(int i = 0; i<= size - 1; i++){
        for(int j = i + 1; j <= size - 1; j++){
            if(matrix[i][j] != matrix[j][i]){
                return false;
            }
        }
    }
    return true;
}

private char[][] convert(List<String> words, int size) {
    int row = words.size();
    char[][] rst = new char[size][size];
    int i = 0;
    for(; i <= row - 1; i++){
        int j = 0;
        for(char c : words.get(i).toCharArray()){
            rst[i][j] = c;
            j++;
        }
        while(j <= size - 1){
            rst[i][j] = ' ';
            j++;
        }
    }
    while(i <= size - 1){
        int j = 0;
        while(j <= size - 1){
            rst[i][j] = ' ';
            j++;
        }
        i++;
    }
    return rst;
}