leetcode 217. Contains Duplicate 287. Find the Duplicate Number 442. Find All Duplicates in an Array 448. Find All Numbers Disappeared in an Array

后面3个题都是限制在1～n的，所有可以不先排序，可以利用巧方法做。最后两个题几乎一模一样。

 217. Contains Duplicate

class Solution {
public:
    bool containsDuplicate(vector<int>& nums) {
        int length = nums.size();
        if(length <= 0)
            return false;
        sort(nums.begin(),nums.end());
        for(int i = 1;i < length;i++){
            if(nums[i] == nums[i-1])
                return true;
        }
        return false;
    }
};

287. Find the Duplicate Number

class Solution {
public:
    int findDuplicate(vector<int>& nums) {
        int length = nums.size();
        if(length <= 0)
            return -1;
        int start = 1;
        int end = length - 1;
        while(start < end){
            int mid = (start + end)/2;
            int count = 0;
            for(int i = 0;i < length;i++){
                if(nums[i] <= mid)
                    count++;
            }
            if(count > mid)
                end = mid;
            else
                start = mid + 1;
        }
        return start;
    }
};

http://www.cnblogs.com/grandyang/p/4843654.html

https://blog.csdn.net/xudli/article/details/48802345

https://segmentfault.com/a/1190000003817671

442. Find All Duplicates in an Array

注意比的时候要i+1，因为数值比坐标大

class Solution {
public:
    vector<int> findDuplicates(vector<int>& nums) {
        vector<int> result;
        int length = nums.size();
        if(length <= 0)
            return result;
        for(int i = 0;i < length;i++){
            if(nums[i] != nums[nums[i] - 1]){
                swap(nums[i],nums[nums[i]-1]);
                i--;
            }
        }
        for(int i = 0;i < length;i++){
            if(nums[i] != i + 1)
                result.push_back(nums[i]);
        }
        return result;
    }
};

http://www.cnblogs.com/grandyang/p/6209746.html

448. Find All Numbers Disappeared in an Array

这个题与442的题代码几乎一模一样，只是result存储的是坐标+1，也就是具体的消失的数值

class Solution {
public:
    vector<int> findDisappearedNumbers(vector<int>& nums) {
        vector<int> result;
        int length = nums.size();
        for(int i = 0;i < length;i++){
            if(nums[i] != nums[nums[i]-1]){
                swap(nums[i],nums[nums[i]-1]);
                i--;
            }
        }
        for(int i = 0;i < length;i++){
            if(nums[i] != i+1)
                result.push_back(i+1);
        }
        return result;
    }
};

https://www.cnblogs.com/grandyang/p/6222149.html