├── Determine Color of a Chessboard Square.txt
├── First letter to appear twice.txt
├── Largest Odd Number in String.txt
├── Longest Common prefix.txt
├── Minimum Operations to Make a Uni-Value Grid.txt
└── Roman to Integer.txt


/Determine Color of a Chessboard Square.txt:
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1 | class Solution {
2 |     public boolean squareIsWhite(String coordinates) {
3 |         return (coordinates.charAt(0) + coordinates.charAt(1)) % 2 == 1;
4 |     }
5 | }


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/First letter to appear twice.txt:
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 1 | class Solution {
 2 |     public char repeatedCharacter(String s) {
 3 |         int[] cnt = new int[26];
 4 |         for (int i = 0;; ++i) {
 5 |             char c = s.charAt(i);
 6 |             if (++cnt[c - 'a'] == 2) {
 7 |                 return c;
 8 |             }
 9 |         }
10 |     }
11 | }


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/Largest Odd Number in String.txt:
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 1 | class Solution {
 2 |     public String largestOddNumber(String num) {
 3 |         for (int i = num.length() - 1; i >= 0; --i) {
 4 |             int c = num.charAt(i) - '0';
 5 |             if ((c & 1) == 1) {
 6 |                 return num.substring(0, i + 1);
 7 |             }
 8 |         }
 9 |         return "";
10 |     }
11 | }


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/Longest Common prefix.txt:
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 1 | class Solution {
 2 |     public String longestCommonPrefix(String[] strs) {
 3 |         int n = strs.length;
 4 |         for (int i = 0; i < strs[0].length(); ++i) {
 5 |             for (int j = 1; j < n; ++j) {
 6 |                 if (strs[j].length() <= i || strs[j].charAt(i) != strs[0].charAt(i)) {
 7 |                     return strs[0].substring(0, i);
 8 |                 }
 9 |             }
10 |         }
11 |         return strs[0];
12 |     }
13 | }


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/Minimum Operations to Make a Uni-Value Grid.txt:
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 1 | class Solution {
 2 |     public int minOperations(int[][] grid, int x) {
 3 |         int m = grid.length, n = grid[0].length;
 4 |         int[] nums = new int[m * n];
 5 |         int mod = grid[0][0] % x;
 6 |         for (int i = 0; i < m; ++i) {
 7 |             for (int j = 0; j < n; ++j) {
 8 |                 if (grid[i][j] % x != mod) {
 9 |                     return -1;
10 |                 }
11 |                 nums[i * n + j] = grid[i][j];
12 |             }
13 |         }
14 |         Arrays.sort(nums);
15 |         int mid = nums[nums.length >> 1];
16 |         int ans = 0;
17 |         for (int v : nums) {
18 |             ans += Math.abs(v - mid) / x;
19 |         }
20 |         return ans;
21 |     }
22 | }


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/Roman to Integer.txt:
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 1 | class Solution {
 2 |     public int romanToInt(String s) {
 3 |         String cs = "IVXLCDM";
 4 |         int[] vs = {1, 5, 10, 50, 100, 500, 1000};
 5 |         Map<Character, Integer> d = new HashMap<>();
 6 |         for (int i = 0; i < vs.length; ++i) {
 7 |             d.put(cs.charAt(i), vs[i]);
 8 |         }
 9 |         int n = s.length();
10 |         int ans = d.get(s.charAt(n - 1));
11 |         for (int i = 0; i < n - 1; ++i) {
12 |             int sign = d.get(s.charAt(i)) < d.get(s.charAt(i + 1)) ? -1 : 1;
13 |             ans += sign * d.get(s.charAt(i));
14 |         }
15 |         return ans;
16 |     }
17 | }


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