lc-960

   public int minDeletionSize(String[] strs) {
        int m = strs.length;
        int n = strs[0].length();
        int[] dp = new int[n];
        int ans = 0;
        for (int i = 0; i < n; i++) {
            dp[i] = 1;
            for (int j = 0; j < i; j++) {
                boolean isValid = true;
                for (int k = 0; k < m; k++) {
                    if (strs[k].charAt(i) < strs[k].charAt(j)) {
                        isValid = false;
                    }
                }
                if (isValid) {
                    dp[i] = Math.max(dp[j] + 1, dp[i]);
                }
                ans = Math.max(dp[i], ans);
            }
        }
        return n - ans;
    }