LeetCode Weekly Contest 258

第一题

class Solution {
    public String reversePrefix(String word, char ch) {
        int index = word.indexOf(ch + "");
        if (index != -1) {
          String s = word.substring(0, index+1);
          StringBuilder stringBuilder = new StringBuilder(s);
          return stringBuilder.reverse().toString()+word.substring(index+1);
        }
        return word;
    }
}

第二题

class Solution {
    public long interchangeableRectangles(int[][] r) {
         int n = r.length;
        double[] rate = new double[n];
        for (int i = 0; i < n; i++) {
          rate[i] = (double) r[i][0] / (double) r[i][1];
        }
        Arrays.sort(rate);
        long res = 0;
        for (int i = 0; i < n; i++) {
          int j = i + 1;
          while (j < n && rate[i] == rate[j]) {
            j++;
          }
          long len = j - i;
          res += (len * (len - 1)) / 2;
          i = j-1;
        }
        return res;
    }
}

第三题

class Solution {
public:
    int ans = 0, n;
    string S;
    bool check(string v){
        int m = v.size();
        for(int i=0; i<m; i++){
            if(v[i] != v[m-1-i]) return false;
        }
        return true;
    }
    void dfs(int u, string l, string r){
        if(u == n){
            int t = l.size() * r.size();
            if(t <= ans) return;
            if(check(l) && check(r)){
                ans = max(ans, t);
            }
            return;
        }
        dfs(u+1, l, r);
        dfs(u+1,l+S[u], r);
        dfs(u+1, l, r+S[u]);
    }
    int maxProduct(string s) {
        n  = s.size();
        S = s;
        dfs(0, "", "");
        return ans;
    }
};