leetcode-25-exercise_string&array

14. Longest Common Prefix

Write a function to find the longest common prefix string amongst an array of strings.

解题思路：

以strs[0]为标准，LCP的长度必不超过strs[0]的长度，从前向后遍历。内层遍历所有的串，如果在所有串中都有strs[0][i]，

就把它放到result中，否则返回。

string longestCommonPrefix(vector<string>& strs) {
        int len = strs.size();
        string result = "";
        if (len == 0)
            return result;
        if (len == 1)
            return strs[0];
        if (strs[0] == "")
            return strs[0];
        for (int i = 0; i < strs[0].length(); i++) {
            for (int j = 1; j < len; j++) {
                if (strs[j].length() == i || strs[0][i] != strs[j][i])
                    return result;
            }
            result.push_back(strs[0][i]);
        }
        return result;
    }

　　

---

219. Contains Duplicate II

Given an array of integers and an integer k, find out whether there are two distinct indices i and j in the array such that nums[i] = nums[j] and the absolute difference between i and j is at most k.

解题思路：

使用unordered_map存储<nums[i], first_i>。如果当前i-first_i <= k，那就找到了。

bool containsNearbyDuplicate(vector<int>& nums, int k) {
        if (k == 0)
            return false;
        unordered_map<int, int> m;
        for (int i = 0; i < nums.size(); i++) {
            if (m.find(nums[i]) != m.end() && i - m[nums[i]] <= k)
                return true;
            else
                m[nums[i]] = i;
        }
        return false;
    }

　

---