287. Find the Duplicate Number

# Answer-1

Runtime   4 ms
Beats    87.86%


Memory   51.8 MB
Beats    99.95%

class Solution {
    public int findDuplicate(int[] nums) {
    for (int i = 0; i < nums.length; i++) {
            int k=Math.abs(nums[i]);
            if(nums[k]<0){System.gc();return k;}
            nums[k]*=-1;
        }
        return 0;
    }
}

# Answer-2

Runtime   3 ms
Beats    92.21%


Memory   57.5 MB
Beats    23.54%

class Solution {
    public int findDuplicate(int[] nums) {
    int count[] = new int [nums.length];
    for(int i = 0; i<nums.length; i++){
        count[nums[i]]++;
        if(count[nums[i]] > 1){
            return nums[i];
        } 
    }
    return nums.length;
    }
}

# Answer-3

Runtime   2 ms
Beats    98.59%


Memory   57.5 MB
Beats    21.82%

class Solution {
    public int findDuplicate(int[] nums) {
        int res=0,i=0,c=0;
        int[] fre=new int[nums.length];
        for(;i<nums.length;i++){
            c=nums[i];
            fre[c-1]++;
        }
        for(i=0;i<nums.length;i++){
            if(fre[i]>1)
                res=i+1;
        }
        return res;
    }
}