[leetcode]304. Range Sum Query 2D - Immutable -- JavaScript 代码

/**
 * @constructor
 * @param {number[][]} matrix
 */
var NumMatrix = function(matrix) {
    var myMatriRow = [];
    matrix.forEach(function(array){
        var rowArray = [];
        array.forEach(function(item,index){
            if(index===0){
                rowArray.push(item);
            }else{
                tmp = item + rowArray[index-1];
                rowArray.push(tmp);
            }
        });
        myMatriRow.push(rowArray);
    });
    this.arraydata = myMatriRow;
};

/**
 * @param {number} row1
 * @param {number} col1
 * @param {number} row2
 * @param {number} col2
 * @return {number}
 */
NumMatrix.prototype.sumRegion = function(row1, col1, row2, col2) {
    var dataArray = this.arraydata;
    var sum = 0;
    for(var i=row1;i<=row2;i++){
        if(col1===0){
            tmpNum = dataArray[i][col2];
        }else{
            tmpNum = dataArray[i][col2] - dataArray[i][col1-1];
        }
        sum += tmpNum;
    }
    return sum;
};


/**
 * Your NumMatrix object will be instantiated and called as such:
 * var numMatrix = new NumMatrix(matrix);
 * numMatrix.sumRegion(0, 1, 2, 3);
 * numMatrix.sumRegion(1, 2, 3, 4);
 */

注意，由于后续的访问都是以sumRegion(0, 1, 2, 3)形式来获取结果的，所以，复杂的代码处理应该放在NumMatrix函数中，将数据格式整理好后，每次调用sumRegion函数就仅需要简单的数据处理了，可以大大提高代码效率。