刷题笔记 Hot100 240. 搜索二维矩阵 II

最直接的想法: 遍历二维数组，找到target

class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        int row = matrix.length, col = matrix[0].length;
        for (int i = 0; i < row; i++) {
            if (matrix[i][0] > target) {
                row = i;
                break;
            }
        }
        for (int j = 0; j < col; j++) {
            if (matrix[0][j] > target) {
                col = j;
                break;
            }
        }
        for (int i = row - 1; i >= 0; i--) {
            for (int j = col - 1; j >= 0; j--) {
                if (matrix[i][j] == target) return true;
            }
        }
        return false;
    }
}

根据题意进行优化:
从左往右递增，从上往下递增，那么可以从左上角开始找
1.若matrix[i][j] == target，则返回true
2.若matrix[i][j] > target，target比当前值小，应该往左边找
3.若matrix[i][j] < target，target比当前值大，应该往下面找

class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        int row = matrix.length, col = matrix[0].length, i = 0, j = col - 1;
        while (i < row && j >= 0) {
            if (matrix[i][j] == target) return true;
            if (matrix[i][j] > target) {
                j--;
            } else {
                i++;
            }
        }
        return false;
    }
}