LeetCode 525. Contiguous Array

525. Contiguous Array

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• Total Accepted: 2476
• Total Submissions: 8220
• Difficulty: Medium
• Contributors: bishwa 

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.

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【题目分析】

这个题目的意思是给定一个只包含0，1的整数数组，找到数组中最长的一个子序列，该序列中1的个数和0的个数相同。

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【思路】

这个题目真的很有意思啊，我感觉自己想不到这么好的解法。

看大家的解题思路如下：

The idea is to change 0 in the original array to -1. Thus, if we find SUM[i, j] == 0 then we know there are even number of -1 and 1 between index i and j. Also put the sum to index mapping to a HashMap to make search faster.

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【java代码】

public class Solution {
    public int findMaxLength(int[] nums) {
        for(int i = 0; i < nums.length; i++) {
            if(nums[i] == 0) nums[i] = -1;
        }
        
        int res = 0, sum = 0;
        Map<Integer, Integer> map = new HashMap<>();
        map.put(0, -1);
        
        for(int i = 0; i < nums.length; i++) {
            sum += nums[i];
            if(map.containsKey(sum)) {
                res = Math.max(res, i-map.get(sum));
            }
            else {
                map.put(sum, i);
            }
        }
        
        return res;
    }
}