leetcode 41. First Missing Positive

看不懂1

var firstMissingPositive = function(nums) {
        var N = nums.length;
        var A = new Uint16Array(N)
        for(var i = 0; i < N; i++)
            if(nums[i]>0 && nums[i]<=N)
                A[nums[i]-1] = nums[i];
        for(var i = 0; i < N; i++)
            if(A[i] != i+1)
                return i+1;
        return N+1;
};

看不懂2

var firstMissingPositive = function(nums) {
    var start = 0;
    var end = nums.length - 1;
    while (start <= end) {
        var index = nums[start] - 1;
        if (index == start)
            start++;
        else if (index < 0 || index > end || nums[start] == nums[index])
            nums[start] = nums[end--];
        else {
            nums[start] = nums[index];
            nums[index] = index + 1;
        }
    }
    return start + 1;
};