Leetcode 525 Contiguous Array
題目原文
Given a binary array, find the maximum length of a contiguous subarray with equal number of 0 and 1.
Example 1:
Input: [0,1]
Output: 2
Explanation: [0, 1] is the longest contiguous subarray with equal number of 0 and 1.
Example 2:
Input: [0,1,0]
Output: 2
Explanation: [0, 1] (or [1, 0]) is a longest contiguous subarray with equal number of 0 and 1.
Note:The length of the given binary array will not exceed 50,000.
題意分析
給一串由0和1構成的數組,求其中0,1個數相同最小數組的長度。
解法分析
當遍歷到0時都看做-1,對所有的元素進行累加,如果加和爲0,則說明前面整個子數組都是0,1相等的子數組,如果和不爲0,則將該和作爲key同相應下標放入map中,若發現加和key存在,則表明從第一次加和爲key時到第二次加和爲key時的元素加和爲0,間隔子數組爲0,1平衡數組,用兩次的下標相減就能得到相應長度,與maxLen比較,取大值。C++代碼如下:
class Solution {
public:
int findMaxLength(vector<int>& nums) {
map<int,int> myMap;
int maxLen=0,count=0;
int i;
for(i=0;i<nums.size();i++){
count+=(nums[i]==0)?-1:1;
if(count==0)
maxLen=i+1;
else{
if(myMap.find(count)==myMap.end())
myMap[count]=i;
else
maxLen=max(maxLen,i-myMap[count]);
}
}
return maxLen;
}
};
改程序的算法複雜度爲O(n)。