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.
/**
* 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 equal number of -1 and 1 between index i
* and j. Also put the sum to index mapping to a HashMap to make search faster.
*/
public class Solution {
public int findMaxLength(int[] nums) {
for (int i = 0; i < nums.length; i++)
if (nums[i] == 0)
nums[i] = -1;
// Map of sum -> index
Map<Integer, Integer> sumToIndex = new HashMap<>();
sumToIndex.put(0, -1);
int sum = 0, max = 0;
for (int i = 0; i < nums.length; i++) {
sum += nums[i];
if (sumToIndex.containsKey(sum))
max = Math.max(max, i - sumToIndex.get(sum));
else
sumToIndex.put(sum, i);
}
return max;
}
}