LeetCode 3、28、1351

//双指针
class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        unordered_map<char,int> hash;
        int res = 0;
        for (int i = 0, j = 0; j < s.size(); j ++) {
            hash[s[j]] ++;
            while (hash[s[j]] > 1) hash[s[i ++]] --;
            res = max(res, j - i + 1);  //维护最大的子串
        }
        return res;
    }
};

//暴力枚举
class Solution {
public:
    int strStr(string haystack, string needle) {
        int n = haystack.length(), m = needle.length();
        for (int i = 0; i < n - m + 1; i++) {
            bool is_same = true;
            for (int j = 0; j < m; j++)
                if (haystack[i + j] != needle[j]) {
                    is_same = false;
                    break;
                }
            if (is_same )
                return i;
        }
        return -1;
    }
};

class Solution {
public:
    int countNegatives(vector<vector<int>>& grid) {
        int num=0;
        for (auto x:grid){
            int l=0,r=(int)x.size()-1,pos=-1;
            while (l<=r){
                int mid=l+((r-l)>>1);
                if (x[mid]<0){
                    pos=mid;
                    r=mid-1;
                }
                else l=mid+1;
            }
            if (~pos) num+=(int)x.size()-pos;// pos=-1表示这一行全是>=0的数，不能统计
        }
        return num;
    }
};