Leetcode First Missing Positive
2014-07-03 17:35
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Given an unsorted integer array, find the first missing positive integer.
For example,
Given
and
Your algorithm should run in O(n) time and uses constant space.
给定无序整型数组,找出第一个不在数组里的正整数,要求时间复杂度为O(n),空间复杂度为O(1)
本题使用数组下标来存储相应的值,比如第k个元素(对应的下标是k-1)存储数字k,也就是A[k-1] = k。
对于大于数组长度的数字或者小于1的数字直接抛弃
一旦有了新数组,就从头开始扫描,遇到第一个A[k-1]不等于k时,输出k,如果没有遇到,那结果只能是数组长度的下一个数
For example,
Given
[1,2,0]return
3,
and
[3,4,-1,1]return
2.
Your algorithm should run in O(n) time and uses constant space.
给定无序整型数组,找出第一个不在数组里的正整数,要求时间复杂度为O(n),空间复杂度为O(1)
本题使用数组下标来存储相应的值,比如第k个元素(对应的下标是k-1)存储数字k,也就是A[k-1] = k。
对于大于数组长度的数字或者小于1的数字直接抛弃
一旦有了新数组,就从头开始扫描,遇到第一个A[k-1]不等于k时,输出k,如果没有遇到,那结果只能是数组长度的下一个数
class Solution { public: int firstMissingPositive(int A[], int n) { for(int i = 0 ; i < n; ++ i){ if(A[i] > 0 && A[i]<=n){ if(A[i]-1 != i && A[A[i]-1]!=A[i]) { swap(A[i],A[A[i]-1]); i--; } } } for(int i = 0 ; i < n; ++ i) if(A[i]-1 != i) return i+1; return n+1; } };
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