LeetCode 474 一和零

 

public int findMaxForm(String[] strs, int m, int n) {
    int length = strs.length;
    int[][][] dp = new int[length + 1][m + 1][n + 1];
    for (int i = 1; i <= length; i++) {
        int[] zerosOnes = getZerosOnes(strs[i - 1]);
        int zeros = zerosOnes[0], ones = zerosOnes[1];
        for (int j = 0; j <= m; j++) {
            for (int k = 0; k <= n; k++) {
                dp[i][j][k] = dp[i - 1][j][k];
                if (j >= zeros && k >= ones) {
                    dp[i][j][k] = Math.max(dp[i - 1][j][k], dp[i - 1][j - zeros][k - ones] + 1);
                }
            }
        }
    }
    return dp[length][m][n];
}

public int[] getZerosOnes(String str) {
    int[] zerosOnes = new int[2];
    int len = str.length();
    for (int i = 0; i < len; i++) {
        zerosOnes[str.charAt(i) - '0']++;
    }
    return zerosOnes;
}
还有空间优化的版本：
   public int findMaxForm(String[] strs, int m, int n) {
        int[][] dp = new int[m + 1][n + 1];
        dp[0][0] = 0;
        for (String s : strs) {
            int[] zeroAndOne = calcZeroAndOne(s);
            int zeros = zeroAndOne[0];
            int ones = zeroAndOne[1];
            for (int i = m; i >= zeros; i--) {
                for (int j = n; j >= ones; j--) {
                    dp[i][j] = Math.max(dp[i][j], dp[i - zeros][j - ones] + 1);
                }
            }
        }
        return dp[m][n];
    }

    private int[] calcZeroAndOne(String str) {
        int[] res = new int[2];
        for (char c : str.toCharArray()) {
            res[c - '0']++;
        }
        return res;
    }