Partition Array

Description

Given an array nums of integers and an int k, partition the array (i.e move the elements in "nums") such that:

All elements < k are moved to the left All elements >= k are moved to the right Return the partitioning index, i.e the first index i nums[i] >= k.

Notice
You should do really partition in array nums
instead of just counting the numbers of integers smaller than k.
If all elements in nums are smaller than k,
then return nums.length

Example
If nums = [3,2,2,1] and k=2, a valid answer is 1.

Challenge
Can you partition the array in-place and in O(n)?
We are here

Link

Lintcode_ladder

Method

1. Similar to the Sort Colors
2. x

Example

1. 1

class Solution {
public:
    int partitionArray(vector<int> &nums, int k) {
        // write your code here
        if (nums.empty()) {
            return 0;
        }
        int n = nums.size();
        int start = 0;
        int end = n-1;
        int i = 0;
        while (i <= end) {
            if (nums[i] < k) {
                swap(nums[i], nums[start]);
                start++;
                i++;
            } else {
                swap(nums[i], nums[end]);
                end--;
            }
        }
        return start;
    }
};

Similar problems

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Tags

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