LCP 19. 秋叶收藏集

解法一：动态规划

参考官方题解：https://leetcode-cn.com/problems/UlBDOe/solution/qiu-xie-shou-cang-ji-by-leetcode-solution/

class Solution {
    public int minimumOperations(String leaves) {
        int n = leaves.length();
        int[][] dp = new int[n][3];
        dp[0][0] = toRed(leaves.charAt(0));
        dp[0][1] = dp[0][2] = dp[1][2] = Integer.MAX_VALUE;
        for (int i = 1; i < n; ++i) {
            dp[i][0] = dp[i - 1][0] + toRed(leaves.charAt(i));
            dp[i][1] = Math.min(dp[i - 1][0], dp[i - 1][1]) + toYellow(leaves.charAt(i));
            if (i >= 2) {
                dp[i][2] = Math.min(dp[i - 1][1], dp[i - 1][2]) + toRed(leaves.charAt(i));
            }
        }
        return dp[n - 1][2];
    }
    private int toRed(char ch) {
        if (ch == 'r') {
            return 0;
        } else {
            return 1;
        }
    }
    private int toYellow(char ch) {
        if (ch == 'y') {
            return 0;
        } else {
            return 1;
        }
    }
}