代码随想录第34天|贪心算法

59.合并区间

class Solution {
public:
    struct cmp{
        bool operator()(vector<int>& a, vector<int>& b) {
            return a[0] < b[0];
        }
    };
    vector<vector<int>> merge(vector<vector<int>>& intervals) {
        if (intervals.size() == 1)
            return intervals;
        sort(intervals.begin(), intervals.end(), cmp());
        int begin = intervals[0][0];
        int end = intervals[0][1];
        vector<vector<int>> res;
        for (int i = 1; i < intervals.size(); i++) {
            if (intervals[i][0] <= end) {
                if (end <= intervals[i][1]) {
                    end = intervals[i][1];
                }
            } else {
                res.push_back(vector<int>{begin, end});
                begin = intervals[i][0];
                end = intervals[i][1];             
                    
            }
        }
        res.push_back(vector<int>{begin, end});
        return res;
    }
};

738.单调递增的数字

暴力解法超时
贪心思路:

例如 98
strNum[i - 1] > strNum[i] 时, strNum[i - 1]减一, strNum[i]赋值9, 结果则是 89
flag 则是避免 100 的情况出现

class Solution {
public:
    int monotoneIncreasingDigits(int n) {
        string str = to_string(n);
        int flag = str.size();
        for (int i = str.size() - 1; i > 0; i--) {
            if (!(str[i - 1] <= str[i])) {
                str[i - 1] --;
                flag = i;
            }
        }
        for (int i = flag; i < str.size(); i++) {
            str[i] = '9';
        }
        return stoi(str);
    }
};