1143. 最长公共子序列

class Solution {
    public int longestCommonSubsequence(String text1, String text2) {
        int l1 = text1.length();
        int l2 = text2.length();
        // dp[i][j]: 长度[0, i-1]的字符串text1和长度[0, j-1]的字符串text2
        int[][] dp = new int[l1 + 1][l2 + 1];
        
        for(int i = 0; i < l1; i++)dp[i][0] = 0;
        for(int j = 0; j < l2; j++)dp[0][j] = 0;

        for(int i = 1; i <= l1; i++){
            for(int j = 1; j <= l2; j++){
                if(text1.charAt(i-1) == text2.charAt(j-1))dp[i][j] = dp[i - 1][j - 1] + 1;
                else dp[i][j] = Math.max(dp[i - 1][j], dp[i][j - 1]);
            }
        }

        return dp[l1][l2];
    }
}

1035. 不相交的线

就是求最长的公共子序列长度，不要求连续。

class Solution {
    public int maxUncrossedLines(int[] nums1, int[] nums2) {
        int l1 = nums1.length;
        int l2 = nums2.length;
        int[][] dp = new int[l1 + 1][l2 + 1];

        for(int i = 0; i <= l1; i++)dp[i][0] = 0;
        for(int j = 0; j <= l2; j++)dp[0][j] = 0;

        for(int i = 1; i <= l1; i++){
            for(int j = 1; j <= l2; j++){
                if(nums1[i - 1] == nums2[j - 1])dp[i][j] = dp[i - 1][j - 1] + 1;
                else dp[i][j] = Math.max(dp[i - 1][j], dp[i][j - 1]);
            }
        }

        return dp[l1][l2];
    }
}

53. 最大子数组和

class Solution {
    public int maxSubArray(int[] nums) {
        // dp[i]:以nums[i]结尾的最大的连续子数组和
        int[] dp = new int[nums.length];
        dp[0] = nums[0];
        int res = dp[0];
        for(int i = 1; i < nums.length; i++){
            dp[i] = Math.max(dp[i - 1] + nums[i], nums[i]);
            res = Math.max(res, dp[i]);
        }

        return res;
    }
}