525. Contiguous Array

Given a binary array, find the maximum length of a contiguous subarray with equal number of 0 and 1.

Example 1:

1Input: [0,1]
2Output: 2
3Explanation: [0, 1] is the longest contiguous subarray with equal number of 0 and 1.

Example 2:

1Input: [0,1,0]
2Output: 2
3Explanation: [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.

1public class Solution {
2    public int findMaxLength(int[] nums) {
3        if(nums == null || nums.length == 0){
4            return 0;
5        }
6        for(int i=0; i<nums.length; i++){
7            if(nums[i] == 0){
8                nums[i] = -1; //先把所有的0变成-1，这样就是求sum为0的最大区间
9            }
10        }
11        int sum = 0, max = 0;
12        HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
13        map.put(0, -1);
14        for(int i=0; i<nums.length; i++){
15            sum += nums[i];
16            if(!map.containsKey(sum)){
17                map.put(sum, i);
18            }else{
19                max = Math.max(max, i-map.get(sum));
20            }
21        }
22        return max;
23    }
24}