lcpBi99

最小和分割

方法一：HashMap

class Solution {
    public int splitNum(int num) {
        String s = String.valueOf(num);
        int n = s.length();
        int[] cnt = new int[10];
        for (int i = 0; i < s.length(); ++i)
            cnt[s.charAt(i) - '0']++;
        StringBuilder sb1 = new StringBuilder(), sb2 = new StringBuilder();
        boolean flag = false;
        for (int i = 0; i < 10; ++i) {
            while (cnt[i]-- > 0) {
                if (flag)
                    sb2.append(i);
                else
                    sb1.append(i);
                flag = !flag;
            }
        }
        System.out.println();
        return Integer.parseInt(sb1.toString()) + Integer.parseInt(sb2.toString());
    }
}

统计染色格子数

方法一：等差数列

class Solution {
    static long[] sum = new long[100002];

    static {
        sum[1] = 1;
        int diff = 4;
        for (int i = 2; i < sum.length; ++i) {
            sum[i] = sum[i - 1] + diff;
            diff += 4;
        }

    }
    public long coloredCells(int n) {
        return sum[n];
    }
}

统计将重叠区间合并成组的方案数

方法一：贪心 + 快速幂

class Solution {
    static int MOD = (int) 1e9 + 7;

    public int countWays(int[][] ranges) {
        Arrays.sort(ranges, (o1,o2)->o1[0] - o2[0]);
        int res = 2, r = ranges[0][1];
        for (int[] range : ranges) {
            if (range[0] > r)
                res = res * 2 % MOD;
            r = Math.max(r, range[1]);
        }
        return res;
    }
}

统计可能的树根数目

方法一：