代码随想录Day36：无重叠区间、划分字母区间、合并区间

无重叠区间

将右边界排序，统计非重叠区间个数

cpp 复制代码

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

将左边界排序，统计重叠区间个数

cpp 复制代码

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

划分字母区间

cpp 复制代码

class Solution {
public:
    vector<int> partitionLabels(string s) {
        int hash[26] = {0};
        vector<int> result;
        for(int i = 0; i < s.size(); i++){
            hash[s[i] - 'a'] = i;
        }
        int right = 0;
        int left = 0;
        for(int i = 0; i < s.size(); i++){
            right = max(hash[s[i] - 'a'], right);
            if(i == right){
                result.push_back(right - left + 1);
                left = i + 1;
            }
        }
        return result;
    }
};

合并区间

cpp 复制代码

class Solution {
static bool cmp(vector<int>& a, vector<int>& b){
    return a[0] < b[0];
}
public:
    vector<vector<int>> merge(vector<vector<int>>& intervals) {
        if(intervals.size() == 1) return intervals;
        vector<vector<int>> result;
        if(intervals.size() == 0) return result;
        sort(intervals.begin(), intervals.end(), cmp);
        int right = intervals[0][1];
        int left = intervals[0][0];
        for(int i = 1; i < intervals.size(); i++){
            if(intervals[i][0] <= intervals[i-1][1]){  //重叠了
                right = max(intervals[i][1], intervals[i-1][1]);
                intervals[i][1] = right;
            }
            else{
                result.push_back({left, right});
                right = intervals[i][1];
                left = intervals[i][0];
            }
        }
        result.push_back({left, right});
        return result;
    }
};