[閒聊 ] Weekly Contest 405

[Rushia (早瀬ユウカの体操服 )]

第一題
給你一個字串s和數字k 把所有的s字串替換成他的索引+k，索引越界就從左邊繼續走。

java code
--------------------------------------
class Solution {
    public String getEncryptedString(String s, int k) {
        StringBuilder sb = new StringBuilder();
        int n = s.length();
        for (int i = 0; i < n; i++) {
            sb.append(s.charAt((i + k) % n));
        }
        return sb.toString();
    }
}
--------------------------------------

第二題
n才10，直接用回溯法窮舉二進制字串，然後把符合條件的加入結果集。

java code
--------------------------------------
class Solution {
    public List<String> validStrings(int n) {
        List<String> res = new ArrayList<>();
        dfs(res, new StringBuilder(), n);
        return res;
    }


    void dfs(List<String> res, StringBuilder curr, int n) {
        int length = curr.length();
        if (length == n) {
            if (isBinaryString(curr)) {
                res.add(curr.toString());
            }
            return;
        }
        curr.append('0');
        dfs(res, curr, n);
        curr.deleteCharAt(length);
        curr.append('1');
        dfs(res, curr, n);
        curr.deleteCharAt(length);
    }

    boolean isBinaryString(StringBuilder curr) {
        for (int i = 1; i < curr.length(); i++) {
            if (curr.charAt(i) != '1' && curr.charAt(i - 1) != '1') {
                return false;
            }
        }
        return true;
    }
}
--------------------------------------

第三題
簡單dp，因為起始點在左上所以一列一列的掃就好。


java code
--------------------------------------
class Solution {
    public int numberOfSubmatrices(char[][] grid) {
        int n = grid.length;
        int m = grid[0].length;;
        int[][] dp = new int[m][2];
        int res = 0;
        for (int i = 0; i < n; i++) {
            int y = 0;
            int x = 0;
            for (int j = 0; j < m; j++) {
                y += grid[i][j] == 'Y' ? 1 : 0;
                x += grid[i][j] == 'X' ? 1 : 0;
                if (dp[j][0] + x > 0 && dp[j][0] + x == dp[j][1] + y) {
                    res++;
                }
                dp[j][0] += x;
                dp[j][1] += y;
            }
        }
        return res;
    }
}
--------------------------------------


第四題
我看了一下感覺是dp 然後看看測資大小我選擇死亡
遇到困難睡大覺




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