代码随想录-贪心算法（435. 无重叠区间、763. 划分字母区间、56. 合并区间）

435. 无重叠区间

class Solution {
public:
    static bool cmp(const vector<int>& a, const vector<int>& b)
    {
        return a[1]<b[1];
    }

    int eraseOverlapIntervals(vector<vector<int>>& intervals) 
    {
        if (intervals.size()==1) return 0;
        sort(intervals.begin(), intervals.end(), cmp);
        int end = intervals[0][1];
        int count = 0;
        for (int i=1;i<intervals.size();i++)
        {
            if (intervals[i][0]<end) 
            {
                count++;
                // end = intervals[i][1];
            }
        }
        int n = intervals.size();
        return count;
    }
};

763. 划分字母区间

class Solution {
public:
    vector<int> partitionLabels(string s) 
    {
        vector<int> ans;
        vector<int> memo(27, 0);
        for (int i=0; i<s.size(); i++)
        {
            memo[s[i]-'a'] = max(memo[s[i]-'a'], i); 
        }
        

        int sum = 1;
        int last = -1;
        for (int i=0; i<s.size(); i++)
        {
            if (last==-1) 
            {
                last=memo[s[i]-'a'];
                if (i==last) 
                {
                    ans.push_back(1);
                    last = -1;
                }
                continue;
            }
            if (i<last)
            {
                sum++;
                last = max(last, memo[s[i]-'a']);
            }
            else
            {
                ans.push_back(sum+1);
                sum = 1;
                last = -1;
            }
        }
        return ans;
        
        
        
    }
};

56. 合并区间

class Solution {
public:
    static bool cmp(const vector<int>& a, const vector<int>& b)
    {
        if (a[0]==b[0]) return a[1]<b[1];
        return a[0]<b[0];
    }

    vector<vector<int>> merge(vector<vector<int>>& intervals) 
    {
        if (intervals.size()==1) return intervals;
        vector<vector<int>> ans;
        sort(intervals.begin(), intervals.end(), cmp);
        int last = intervals[0][1];
        int first = intervals[0][0];
        for (int i=1; i<intervals.size(); i++)
        {
            if (intervals[i][0]<=last)
            {
                first = min(first, intervals[i][0]);
                last = max(last,intervals[i][1]);
            }
            else
            {
                ans.push_back({first, last});
                first = intervals[i][0];
                last = intervals[i][1];
            }
            if (i==intervals.size()-1) ans.push_back({first, last});
        }
        return ans;

    }
};