First Missing Positive
Description
Given an unsorted integer array, find the smallest missing positive integer.
Example 1:
Input: [1,2,0] Output: 3
Example 2:
Input: [3,4,-1,1] Output: 2
Example 3:
Input: [7,8,9,11,12] Output: 1
Note:
Your algorithm should run in O(n) time and uses constant extra space.
Solution(javascript)
/**
* @param {number[]} nums
* @return {number}
*/
var firstMissingPositive = function(nums) {
const len = nums.length;
let middleman;
for(let i = 0; i < len; i++){
while(nums[i] > 0 && nums[i] <= len && (nums[nums[i]-1] != nums[i])){
middleman = nums[nums[i]-1];
nums[nums[i]-1] = nums[i];
nums[i] = middleman;
}
}
for(let i = 0; i < len; i++){
if(nums[i] != i+1){
return i + 1;
}
}
return len + 1;
};