eg:1,2,4,7,10,11,7,12,6,7,16,18,19 索引是3、9 返回值是7

public static int getMinLength(int[] arr) {
        if (arr==null|| arr.length<2) {
            return 0;
        }
        int min = arr[arr.length-1];
        int noMinIndex = -1;
        for (int i = arr.length-2; i >= 0; i--) {
            if (arr[i]>min) {
                noMinIndex = i;
            } else {
                min = Math.min(min, arr[i]);
            }
        }
        if (noMinIndex==-1) {
            return 0;
        }
        int max = arr[0];
        int noMaxIndex = -1;
        for (int i = 1; i < arr.length; i++) {
            if (arr[i]<max) {
                noMaxIndex = i;
            } else {
                max = Math.max(max, arr[i]);
            }
        }
        return noMaxIndex-noMinIndex+1;
    }