满分答案

Solution.java

// you can also use imports, for example:
// import java.math.*;
class Solution {
  	int equi(int[] a) {
		final int b = a.length;
		long left = 0;
                long right = 0;
		
		for (int i = 0; i < b; i++) {
			right += a[i];
		}
		
		for (int i = 0; i < b; i++) {
			right -= a[i];
			if (left == right) {
				return i;
			}
			left += a[i];
		}
		return -1;
	}
}