[565. Array Nesting] C++ - Unordered_set or Vector or in-place change (O(1) space)


  • 0
    //O(1) space:
    class Solution {
    public:
    int arrayNesting(vector<int>& nums) {
        if(nums.empty()) return 0;
        int res = 0;
        for(int i = 0; i < nums.size(); ++i){
            if(nums[i] == -1){
                continue;
            }
            int tmp = 0;
            int k = i;
            while(nums[k] != -1){
                tmp++;
                int tmp2 = nums[k];
                nums[k] = -1;
                k = tmp2;
                
            }
            res = max(res, tmp);
        }
        return res;
    }
    };
    
    //vector
    class Solution {
    public:
    int arrayNesting(vector<int>& nums) {
        if(nums.empty()) return 0;
        int res = 0;
        vector<bool> check(nums.size(), false);
        for(int i = 0; i < nums.size(); ++i){
            if(check[i]){
                continue;
            }
            int tmp = 0;
            int k = i;
            while(!check[k]){
                check[k] = true;
                tmp++;
                k = nums[k];
            }
            res = max(res, tmp);
        }
        return res;
    }
    };
    
    
    //Set
    class Solution {
    public:
    int arrayNesting(vector<int>& nums) {
        if(nums.empty()) return 0;
        int res = 0;
        unordered_set<int> st;
        for(int i = 0; i < nums.size(); ++i){
            if(st.find(nums[i]) != st.end()){
                continue;
            }
            int tmp = 0;
            int k = i;
            while(st.find(nums[k]) == st.end()){
                st.insert(nums[k]);
                tmp++;
                k = nums[k];
            }
            res = max(res, tmp);
        }
        return res;
    }
    };

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