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.
把nums[]里所有的0改成-1，累加nums[i]并且记录索引index，当sum值再次出现的时候，说明中间的0，1数量相等。代码如下： public class Solution { public int findMaxLength(int[] nums) { if (nums.length == 0 || nums == null) { return 0; } for (int i = 0; i < nums.length; i ++) { if (nums[i] == 0) { nums[i] = -1; } } HashMap<Integer, Integer> map = new HashMap<Integer, Integer>(); int sum = 0, max = 0; map.put(0, -1); for (int i = 0; i < nums.length; i ++) { sum += nums[i]; if (map.containsKey(sum)) { max = Math.max(max, i - map.get(sum)); } else { map.put(sum, i); } } return max; } }